Turn garbage disposal waste into compost?

hup2345(z6 NY)October 24, 2008

Hi Composters,

I'm new to this forum, but have been on the Roses forum many years. I am an avid gardener. I come to you with a question. Does anyone know of a way to trap the output of a kitchen garbage disposal, divert the ground-up waste, and convert that into compost? If a device/system doesn't already exist, I'd like to take a crack at it. Seems to me that this is an invention just waiting to happen.

Your input is greatly appreciated.


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billhill(z5 MI - KBG)

Although the concept is excellent, I think that would be more trouble than it would be worth. Many keep a small container in the kitchen for scraps that would otherwise go into the garbage disposal unit. I use a red plastic coffee can. Many use a more beautiful decorative container. Vegetable waste goes into the can. The contents of the can goes into a 5 gallon bucket in the garage and later gets buried in the back yard compost pile or bin. If you dont have a compost pile then you could consider vermicomposting using worms. There is another forum dedicated to vermicomposting. Kitchen waste is very good stuff to make compost with. I wish I could get more of the stuff.
Bill Hill

    Bookmark   October 25, 2008 at 6:20AM
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As Bill has already stated for people that use a garbage disposal some kind of diverter would be much more trouble than it would be worth. Your diverter would need to be able to allow the waste water from what ever is happening in the sink to flow regularly but be diverted when garbage was being run. There are already systems in place for people that reuse the grey water produced at that point which would include what comes from the disposer, and that would be about the only way a diverter could really work.

    Bookmark   October 25, 2008 at 6:36AM
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rj_hythloday(8A VA)

Like Bill Said I keep a gallon ice cream bucket under the sink. I fill it w/ vegetable scraps, table scraps excluding meat/dairy. When It's full I take it out by the compost pile and put a new one under the sink. Every few days I turn the pile and bury the buckets in the middle of the pile.

    Bookmark   October 25, 2008 at 7:55AM
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Chances are it would violate all sorts of plumbing codes as well.

I agree with the bucket approach. If you like to scrape/peel/cut into the sink, just wait until you're done and grab the stuff and put it in the bucket. If you miss a few carrot peels, so be it. You'll get 90%, and that's pretty good.

    Bookmark   October 27, 2008 at 9:55AM
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gardenlen(s/e qld aust)

too easy a1,

save the kitchen scraps daily and then tuck them in under your garden mulch daily, saves on power & water using the waste disposal unit, and adds necessary nutrients to the garden soil for healthier plants.

or alternatively if you wish to go that way get a worm farm started.


    Bookmark   October 27, 2008 at 2:11PM
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Since the whole idea of getting rid of scraps in the kitchen composter is to wash it down the drain after the blades have a whack at it, I see no reason to try to retain any of it.
If the homeowner had any thought to try to save some kitchen craps, then a separate container under the sink must be thought of and separate that material that fits the description.

In some jurisdictions kitchen under-sink disposals are not allowed because they send too much bad water into sewers.

    Bookmark   October 27, 2008 at 2:43PM
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val_s(z5 central IL)

I'm holding up my hand for the ice cream bucket under the sink. I used to think I wanted a garbage disposal but ever since I started composting, I can't imagine having one. Everything in our kitchen goes either in the bucket, the garbage or the dog's bowl :-)


    Bookmark   October 27, 2008 at 2:55PM
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The recommendations to use a bucket under the sink as the most direct and straightforward way to go about things can't be argued with, but what they discount is that we are all a bit lazy. That, after all, is why in-sink disposals exist in the first place. I consciously avoid putting stuff in the disposal because it is not good for the sewer system and I have often pondered whether the disposal drain could be routed to a compost set-up. It would be complicated to make it work right but there would be benefits that could make it worthwhile. Mostly, you would use it because it was convenient, whereas many people start out with the best of intentions but may not stick with it because the tubs under the sink wind up being smelly, again because they are not really hard core enough to empty them often enough, etc.

I agree that most anything I have dreamed up in this department would not meet code. However, building codes are not known for catering to the fringe. It is possible to build things safely and well that don't meet codes intended to get everyone to meet the least common denominator. I think that you must start with a conventional drain system and then modify it, making sure that you can put it back if necessary.

I envision installing a small sump with a macerating pump under the sink or in the basement. These devices are intended for use when you have appliances that are below the level of the gravity drained sewer. The waste from toilet, shower, and sink flow by gravity into the sump. A float operated switch turns the pump on when the level is high enough. The macerating pump handles solids well. The waste water from the disposal will contain large amounts of solids that must be moved horizontally a long ways such as out to the back yard. Gravity flow would not work dependably for this. The pump will therefor handle both the solids and the need for positive, possibly uphill, movement. The sump/pump combo is designed to stop sewer gasses and pests from backing up and it is ready made and off the shelf.

What to do with the food laden wastewater once you get it to the back yard? A downside of the sump is that due to its large volume, stuff could get rancid between uses so that the water you pump to the back yard could smell, maybe. I don't really know except that on occasion I have left dishes in the sink and the water in them can smell. Obviously, get the smallest sump possible and run lots of water through it to flush it. On the other hand we have still not addressed exactly how we are going to handle the wastewater. I think that if you had a large enough pile of organic matter and you piped the wastewater into the middle of it in the modest quantities we are talking about, that smell would not be a problem. After all if you can compost a horse carcass without smelling it, a few tabel scraps should be a snap. The trick in either case is maintaining a large enough layer of actively composting material. This layer of working compost literally captures and composts the nitrogen rich gasses that carry the smell.

In my opinion, that is the crux of the situation. You must generate as small an amount of wastewater as possible, as rich in scraps as possible. I think it is inevitable that this gray water will be smelly sometimes so you will have to assume it will always be smelly. You must have a large enough pile of compost that it can handle the periodic influxes of smelly stuff, and it must somehow have built into the center of it a hollow space where food scraps and water can accumulate until the water drains down into the soil. I see no economical way to make a system that automatically separates the food from the water and then turns the pile, so you will have a nasty smelly core in the center but again, if various states can compost road-killed deer, you can compost kitchen scraps as long as you keep a garden variety compost mound happily composting on top. I am picturing a tipi like affair a couple of feet high with the usual grass clippings and dead leaves mounded up over the top, or a couple of straw bales with a gap in between.

There are some alternatives. If you could figure a way to use only gravity feed and you can assure that no one puts sour milk down that drain then the potato peels and broccoli stems that you are flushing would probably not pose a smell problem and could be dumped right on top of a compost heap, although you would have to go outside regularly to throw some cover materials on. Also you would have to contend with excess water unless you were diligent about using only the minimum amount of water. The other route to take would be to allow the scraps to collect in the bottom of the sump, let the water overflow the top into the regular sewer, then carefully pump the slurry of solids off the bottom. This would reduce the amount of water, which would be smelly and could leak out of the compost pile. However you would need to maintain that compost pile/organic odor control system described above.

An accepted form of composting is to simply bury the scraps in the garden. Perhaps you could dig a hole in the garden and pipe the slurry to that, with some kind of cover to keep people and pests out. Once a month, dig a new hole and fill in the old one.

Seeing how long this post is, maybe it is more trouble than it's worth.

    Bookmark   October 28, 2008 at 8:03PM
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val_s(z5 central IL)

Mark - while I got a little lost in all the sumps, pumps, codes and drains......I briefly thought your idea indeed was great. I was ready to sign up for one. Especially when I thought about not having to actually tread out to the compost pile through the snow. Then I kind of came to my senses when I realized I'd have to tread out there anyway to throw in the leaves (or shredded paper) that I use to cover the "greens".

I'm thinking the critters around here would like it though if only kitchen waste pumped out to the compost bin. (grin)


    Bookmark   October 28, 2008 at 8:45PM
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On second thought it is too complicated to make it a continuous composting process. You could however make a small leach pit or "cesspool" just for the disposal waste. There won't be any of the fecal bacteria to contend with that are the reason regular cesspools are bad. So, just drain your disposal to this leach pit (covered of course to exclude pests and also with a compost pile on the top of it to treat any escaping odors) for a few months. When the weather is nice and you have a lot of browns handy, then you can dive in and mix up a batch of compost. By this I mean dig the collected scraps out of the leach pit and make a separate compost pile. In other words, it would be easier to make it a batch process that you have to deal with only once in a blue moon. In this regard it would be like having the container under the sink but you don't have to bend down, wrestle with the container, brave the smells and fruit flies, or go outside except every few months.

    Bookmark   November 5, 2008 at 7:35PM
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For the past 25 years my parents have lived on a farm here in Austin. They are by far from poor, but never had a disposal. I never could figure out how they lived without it until much later in life. Everything went into a big plastic pale thing by the sink. Scraps, peeling, shells, tea bags, etc. However they didn't compost. They would just go chunk the entire thing in the yard and the peacocks, chickens and ducks had it taken care of in no time. They also had dogs so they got the meat scraps. Now that I have a house (and compost), virtually nothing goes down my drain.

Now I wonder why they don't have an automatic ice maker! Seriously, their both past 75 and they're bending over cracking those silly ice trays, or buying bagged ice.

    Bookmark   November 5, 2008 at 8:02PM
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Sink strainers are amazing things.

I'm on my own septic and no kitchen wastes go down the drains. When the sink drains poorly,I dump the contents of the strainer into my kitchen waste compost container in the kitchen.

The strainer get's all of the things that the scrapping and soaking don't and garbage disposals are not needed.

    Bookmark   November 5, 2008 at 8:27PM
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toxcrusadr(Zone 6a - MO)

Commercial cafeterias and restaurants have just this sort of beast. It chops up the food waste like a disposer but then filters it out rather than washing large quantities down the drain. The strainer can be removed for emptying.

I concur with the ice cream bucket. The only thing that would really need to be chopped up like that is bones, which aren't that helpful in compost anyway.

    Bookmark   November 6, 2008 at 4:07PM
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I agree this is an invention just waiting to happen altho I'm not holding my breath. IMO it would be a major process to change codes so it would be allowed. When we built here on a large acreage a few years ago I inquired about having the house plumbed so the grey water could be used for flower beds and, of course, the answer was "against code". The other thing that's "against code" here is having an outdoor privy if one has indoor plumbing! I don't really understand that "either/or" connection but I really wanted that little house out beyond my garden so I didn't have to remove my boots when I wanted to "go". Of course, this long after we could probably build one and no one would ever be the wiser.

About the kitchen disposal, I've never wanted one but use a gallon ice cream container and dump the contents in the compost bin once a day after our evening meal. No odors, just a short walk, and good compost for the garden. If everyone did that, just think what our world would be like.

    Bookmark   November 6, 2008 at 7:28PM
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Yep, bucket is best, if you dont put it down the disposal, you neednt worry about getting it OUT of the disposal.

    Bookmark   November 7, 2008 at 9:40AM
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toxcrusadr(Zone 6a - MO)

Luckygal, sure you could build that outhouse! It's called a garden shed. As far as anyone knows. :-]

    Bookmark   November 7, 2008 at 11:19AM
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I have wished for the same thing....thoughts of centrifuges with plumbing....It all does get quite complicated...

I think Mark made a good point when he said we are all lazy (or at least many of us...myself included). In addition, when it has been a while since the "coffee can" was dumped...opening it up to add more scraps is far from pleasant.

What about a "garbage shute" on the wall next to the kitchen sink. It would be a lot simpler and would at least be a way to have the majority of the smell be outside? I'm sure there would be some details to iron out....like sealed cap on the inside, and a gravity flap at the outside outlet. Anyone know if such a thing exists?

    Bookmark   May 3, 2009 at 4:44PM
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I saw in some magazine years back someone built a diverter that sent the muck from the disposal to a barrel in the basement.(which she would pour into compost every couple of days).

    Bookmark   May 3, 2009 at 5:34PM
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Buy a Vitamix!

Scrape, chop, dump. Bypass the disposal.

    Bookmark   May 3, 2009 at 6:53PM
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Some areas of this country already have codes that allow the use of grey water, which water from your kitchen sink and garbage disposal would be, as irrigation water, and there are people that know how to make diverters for that, reroute the grey water, water from your shower, lavatory, kitchen sink, washer, from that which would be black water, the waste from a toilet, so the grey water could go out into the soil.
Since it is not terribly easy to do and requires changing much of your plumbing the simplest thing is to just not use the garbage disposal and put that waste in a bucket to do into a compost bin.

    Bookmark   May 4, 2009 at 8:00AM
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Hang on everyone! I'm working on the patent now. There are few things I have worked out. The compostables will only be diverted while you have your foot on the pedal to engage the diverter. The diverter will allow normal operation when not engaged and all will be BEFORE the P-trap so codes would not be an issue. Lastly, the collection pail can be hooked up to the garden hose before it's opened up in the compost heap for burial. You can empty it withoiut getting your hands dirty. Minimal liquid. No smell.

    Bookmark   August 21, 2009 at 11:08PM
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Nobody mentioned that the scraps ground up in a disposal would presumably compost faster. Maybe much faster for items like grapefruit skins.

    Bookmark   July 6, 2010 at 8:52AM
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If you want your scraps chopped/diced/minced for faster decomposition, the fastest, cheapest method might be to put them through a blender or food processor.

    Bookmark   July 6, 2010 at 12:57PM
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We need household-size anaerobic digesters. Many homes in developing countries have them. ADs produce methane, which of course is used for cooking, heating, & electrical generation. Big business does not want us to know about this in the U.S.

- Always a Conspiracy :]

    Bookmark   February 6, 2011 at 1:16PM
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It is not cheaper,but to answer your question.
You will need a spare sink mounted on a cabinet with a spare disposal, but no drain line. Instead of a drain line you need a 5 gallon bucket, to caught the grind up food. You will have to have a plug to run this outfit.
It would be cheaper to buy a chipper or leaf shredder, which you could...... also shred leaves with!
But that is what you ask for, so there it is.
Good Luck & yes, I thought of the same thing & went with the shredder instead.

    Bookmark   February 7, 2011 at 4:07AM
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Hey hup,
You live in NY, so I assume you might have a basement. I live in TX and have a house built on pier and beam. I keep my compost pile underneath my house, directly under the kitchen. I can easily access the 3" pvc drain line coming from the kitchen sink. If you put a T fitting on the drain line, with either a manual or electric pvc ball valve below the T, you could easily direct your chopped compost directly into your pile. You could even put a sensor on the end, so that after the waste is dumped on the pile, a layer of carbons (I use shredded cardboard) is layered on top. No smell, no hassle, easy as pie. Note: electric ball valves are VERY expensive... As for code; who knows and who cares...chances are it will never be an issue. If it becomes one, play dumb and smile :)

    Bookmark   August 3, 2013 at 10:19AM
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nancyjane_gardener(Zone 8ish North of San Francisco in the "real" wine country)

My disposer died about 5 years ago. I only replaced it when I remodeled for resale value.
Small decorative pot on the counter for immediate use, emptied into about a gallon sized and emptied about every other day. Oh yeah, I spend about 30 seconds with a good sharp knife when I'm cooking to make those pieces smaller! Nancy

    Bookmark   August 4, 2013 at 9:23PM
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toxcrusadr(Zone 6a - MO)

Inked, did you notice the original post was from 2008? Nothing wrong with reviving a thread but the original poster may not be around anymore.

I chop veggie waste a bit and it does just fine in the compost pile. To each his own, but it seems like a lot of trouble to set up a whole disposer just for food waste.

    Bookmark   August 6, 2013 at 10:51AM
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Like Bill and Kim, I also have a small tupperware in my kitchen sink where all food wastes which I eventually throw at the small compost pit I dug at my backyard. Organic fertilizer I got working for my tomatoes.

    Bookmark   August 6, 2013 at 11:34AM
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I see back in '08 "Dr.Doorlock" said (perhaps facetiously) that he was working on a patent for this. I wonder if he ever did it? I can't find contact info for him to ask. I think it's a great idea!

    Bookmark   January 11, 2014 at 1:11PM
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toxcrusadr(Zone 6a - MO)

Another option that may or may not have been discussed in this thread (I didn't reread the whole thing) is to have an old sink with a disposer mounted in a wood frame outdoors. Put a bucket under it and run stuff through.

I still think the shredding is unnecessary, and if you have volume big enough to want to compost it fast you are probably a commercial operation (restaurant etc.) anyway and you can install a commercial one with a removable strainer.

Nothing wrong with the idea for the device, more power to ya, it's just my 2 cents and YMMV.

    Bookmark   January 14, 2014 at 1:25PM
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pipperee(6a / 6b eastern WA)

An extra sink to shred scraps for a household pile might be excessive, but considering the commercial trend towards all things 'green', I think a separate sink/shredder is a great, but simple and inexpensive idea, to speed up the process for mass quantities of scraps for new, or adaptable, restraunteurs (or grocery stores, school cafeterias, etc) that have space to compost. Onsite herb and vegetable gardens are taking off with restaurants even in my not-trendy area, so I imagine onsite composting (with excellent odor management) won't be far behind.

And since this thread started in 2008, a lot of local codes are being updated to accommodate more 'creative' (traditional) ways of managing liquid and solid waste.

Old thread, but still interesting.

    Bookmark   January 15, 2014 at 2:03AM
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Keep in mind that the waste from the kitchen sink, and the disposer, would be considered gray water and some places are now encouraging the recycling of that gray and using that to water your garden.
Running the "waste" food through a garbage disposal is generally a waste of energy.

    Bookmark   January 16, 2014 at 6:45AM
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This seems like an elegant solution:

    Bookmark   March 26, 2014 at 9:27PM
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toxcrusadr(Zone 6a - MO)

This is a great setup if you have the space and are fairly handy. I don't really buy the 'compost in 3-6 days' claim, but it's a minor point.

    Bookmark   March 27, 2014 at 1:24PM
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All you need to do is not put it in the disposal. What I do to my kitchen scraps is run them thru my hamilton beach big mouth juicer which does an excellent job. I save the pulp in a canister for my red wiggler worm bin. In a few days its ready to feed them when they need it.

    Bookmark   March 27, 2014 at 6:34PM
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Ah yes I was going to mention the blender idea if I didn't see it in the thread, but here it is at the end mentioned by hummersteve (and sorry if I missed someone else's comment earlier in the thread).

I haven't seen the end result of how fine a garbage disposal turns scraps into, but a blender can certain liquefy scraps and thus make it easier to compost or even add into a worm bin, as well as for trenching (thought admittedly, for some of those methods, you don't need to liquify).

Another thing I like to do is that before the scraps go into the scrap bowl, I will also cut it up even more into smaller pieces.

I do a similar thing with scraps from the yard. I keep a scissor handy for my yard work, and when I get long pieces of scrap, I cut them into smaller pieces before tossing them into the compost bin.

    Bookmark   March 28, 2014 at 10:56AM
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Suzi AKA DesertDance Zone 9b

Grey water is a great idea. Our water is so hard we bought a whole house soft water system. We can't water plants with it. We are on septic, and I worry that the septic field will be filled with salt...... Can't win!

I just keep my garbage in a plastic bag in a bowl on the sink and dump it in the compost when it's full. No room under the sink.

    Bookmark   March 28, 2014 at 11:37AM
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I did see a small add for just what you were asking for it was a in line basket that would catch solids out of the sewer line after the disposal and then pulled a drawer out the side of this catchment and store it in the bucket under the sink or run it out to you compote or compost pile I personally prefer to use a rotory compost tumbler so it is a sealed system and so I need not worry about meats the add was in Mother Earth News Magazine I will look up issue and pg. # and post it here or give it to people who email me and mention this forum

    Bookmark   August 17, 2014 at 3:55PM
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toxcrusadr(Zone 6a - MO)

When the OP said he was working on a patent, he said the diversion would be installed 'before the P-trap so codes would not be an issue." I don't know for sure but I think if I asked a local building inspector about that, he'd say you can't run drains anywhere but the sewer. Not to be a wet blanket, and I'm all for changing those codes for graywater. Of course if you do it yourself in an existing home, the inspector never sees it. I may do something like this myself. On new construction though, verify what's allowed before building it and taking the chance of having it rejected.

    Bookmark   August 18, 2014 at 2:39PM
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Since this is such an old thread anyway.......

I have a lifestyle block, with my compost and garden both at a lower head than my kitchen sink. I am planning on sending my insinkerator waste (which is on the smaller side of a double sink) and associated grey water (slurry) directly onto the compost heap. The food waste will fall onto the compost and then the water will drain from the bottom of the heap and be directed straight onto my garden.

Other than local code issues (which I can easily circumvent) I can't think of any other pitfalls, and keen to hear anybody's views on this.

(Before you comment about the difficulty of setting this up not being worth the effort etc etc, please note that I do not want to walk my scraps to the compost heap everyday and looking for a lazy system..... I am more than happy spending the effort to set it for the long term returns.....)

    Bookmark   March 13, 2015 at 1:09PM
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toxcrusadr(Zone 6a - MO)

Depending upon the volume of water, your compost can easily become too wet. Compost should be damp, not soaked, and if it's too wet chronically, the water excludes air, and the pile becomes anaerobic which is not a good idea.

Have you considered a 5-gal bucket near the back door, which you can take to the compost bin once in awhile? Or, if you have an upper story deck, put a compost pile or bin below it and drop your kitchen waste into it without having to go downstairs. :-]

    Bookmark   March 16, 2015 at 3:53PM
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