If the tank can be removed here is one method to get rid of the rust: buy a large container of BBs, and dump them into the tank. Put in a bit of gas and shake the *&%# out of it. Empty it and repeat until the the gas comes out clear. I don't know about relining the tank, perhaps someone else would have a solution.

tombob.....The idea about the BB's is worth a try. Do you think a weak solution of muriatic acid would work better than gasoline?

simple and cheap solution, on garbage day drive around until you see a junk lawn mower sitting on the curb. remove the tank and put it on your tiller.

Motorcycle shops sell a product called "Kreem". You can actually buy it from several websites as well.

It comes as a kit and tells you how to clean, etch and seal the tank.

I've done it on a few motorcycle tanks. One was done at least 12 years ago and it still looks like I did it yesterday.

muriatic acid will burn a hole in a 'weak' spot. I would buy the kreem, and follow direction's.

Like machiem's product i used por15 cleaner/sealer. 5 years so far.
I used aquarium gravel to prep for the cleaning.