I assume you are unsure about cutting holes in your liner. Cutting a hole or two is no big deal - but if you are not comfortable with it - you could probably install the skimmer inside the liner. You probably need to weight it down with a couple rocks or it will float. Like you said; you have to find a way to route the piping. I would recommend flexible PVC in the 1.5" to 2" diameter in your flow rate. It is very heavy duty and can withstand our winters.
I am in Green Bay if you are near there.
Jeff

It is possible to install the skimmer inside the liner but not desirable. As Jeff stated,one problem is that they will float. This is especially true if you have filter pads above the pump area. I tried this once and even put solid landscape blocks in the bottom and it still floated. Another problem with in pond skimmer is that some of the floating debris will collect around and behind the skimmer box.

As Jeff mentioned you should be using PVC and it is designed to be buried in the ground. They make a flexible PVC that works fine and I use it for all my pond plumbing which uses 1 1/2" or smaller pipes. If you decide to use that and have to use any fittings I advise you to use electrical PVC fittings instead of the normal white fittings. Properly glued PVC fittings will withstand the normal shifting caused by freezing and thawing.

One thing that I'm not clear about is what you have in the pond. Is it a water garden with just plants or do you have fish as well? With respect to circulation at the bottom of the pond, if you want to do this to keep the bottom clean you may be successful but the result will be cloudy water. Skimmers are not designed to handle the stuff that sinks to the bottom of the pond (fish poo decaying plant material and mulm) they are designed to collect the stuff that floats. You should have some other kind of filtration to deal with the sinking stuff. When the bottom stuff gets pulled into the skimmer and goes through the pump it gets ground up to finer and finer particles and if you don't have a filter to remove it the it just circulates around your pond and the water gets more and more cloudy. Does your waterfall have any kind of filter?

Hope this helps.

THANK U!!! Yes that is very helpful - guide books leave out the plumbing entirely and I could spend hours.... in fact I have... going online trying to figure it all out. It helps to know what the name of the thing is I want to get!

What I want to find now is some kind of fitting to connect two parts of a hose so they screw together like a garden hose onto a faucet - does such a thing exist? And what is that thing called?

Yes - it is called a "Union" and Fleet Farm carries them. Menard's and Home Depot probably have them as well.

Jeff