We're putting a ZZ4 into a 65 Chevelle. The gas tank hasn't had gas in it for over 10 years. Took tank off and can see orange grit on bottom of tank through sender hole. What is the best way to get it thourghly clean? Tried garden hose and nozzle but not enough
pressure.

Send it out and get it boiled , radiator shops normally have the set up to do it, L89SEDAN

I have given up on manual rust removal.... our acid-dipper in town, charges $30 and it comes back like new!