Any tips on cleaning out the gas tank?

My car was a little fuel starved... discovered debris from sitting for four years.

.....I take mine to a good"RADIATOR"shop!
(cool results)

Frictional grinding is a good choice

Click to view attachment

several superabrasive products are on the market (See Pic.)

Fixing the tank to an old concrete mixer to rotate it, is a cheap and easy way.

I put a bunch of all nuts and bolts in it and shake it around vigorously until I am satisfied with the results. Then, I coated mine.

I have a box of crushed walnut shells...

Walnut shells lack mass. Fasteners are heavy.

Another choice is a few lbs. of drywall screws; nice sharp, shake the thing around for a few min., and dump them out. I'v also used short length's of chain, followed by acetone rinse, and had very good luck with adhesion.

I have used a piece of chain and lacquer thinner...

Chain was easier to get out then lots of little fasteners.

But if you cannot pick up the tank and turn it around, a radiator shop will boil it out for a fee.

I agree have it boiled out at a radiator shop, well worth the cost. If your DIYing then sharp gravel is an option

turns out the tank was clean inside, and somehow my suck-side fuel line to my fuel pump found its way between the tank and the body. :-)