Cleaning Portable Metal Tanks

[zelek]

Does anyone have any ideas on the best way to clean old varnish-like gas residue from the inside of a portable metal fuel tank?? There doesn't appear to be any rust in it and it's in real good condition.

I got this one for nothing and would like to use it, if possible, rather than forking over $85 for a new one.

[Surface Tension]

If its hardened varnish then its stabilized and can't hurt anything. Just rinse out the tank with gas and you should be good to go.

[zelek]

It's got about 1/4" of very old gas in it and it when you tilt it to one side the bottom has some gunk on it. I was told heating up the bottom after adding a little vinegar to it will help?? I'm not so sure I want to experiment though and screw up my outboard now that it's running so well.

Should I just rinse it out thoroughly with fresh gas and call it good, or is there a proven technique that involves something else??