A buddy gave me an old trail bike and the tank was left with gas in it. The gas had turned to varnish stunk like hell and has left a mess in the tank. I drained it and was wondering if anyone new the best way to clean out the tank. I was thinking maybe kerosene or something along those lines.

 

If you search on line,I think there may be products to clean tanks.If not.I would just rinse it with gas(in a safe area)a few times.
Buy a cheap clear inline fuel filter.

If the tank is that bad,I would suspect the carb is gummed up as well.

 

You could spray a bunch of carb cleaner in it and leave it set overnight.

 

I seem to remember that 100LL avgas will desolve it , but not sure how long it will take. Whatever you play with make sure it won't eat the paint if you spill some on it.
Ron