Re: how to clean small outboard gas tank?
When I get an antique outboard with gummy tank, I put in a can of B-12 chemtool and let it soak for a few days. Then I empty it and take it to the car wash for a high pressure rinse. If any crud remains I put in a mixture of HOT water and a 100 or so BB's (count them). Then I put the cap on and shake, shake, shake until I can't shake anymore. That generally breaks up the crud, be sure the exact number of BB's you put in comes back out. Then I pressure rinse again. May have to repeat this process until the inside looks clean, using a small flashlight to see down in there. Nuts and bolts work too, but they can get stuck in odd corners if you are unlucky and have some kind of structure inside the tank. DO NOT do the nuts and bolts and chemtool thing in a metal tank. One spark is one spark too many and not worth risking. After its clean, run a couple of bottles of rubbing alcohol through it to evaporate out any remaining water, then use a blow dryer to dry it out. Good luck with the petcock, you may be able to degum/free it up by soaking in chemtool for a loong time. After you get it clean as you can, install a fuel filter between the tank and the pump...just good insurance.