You can do a 4 hr presure drop test at 1 or 2 psig (no more than 50% of tank rating on nameplate) by sealing all fitings at tank and rig a pump and valve, then close valve. Soapy water test all sealed fittings be be sure they are sealed especially fuel sender. A foot actuated bike/car tire pump may be used with proper fittings.
No need to drain fuel, but if it leaks at the bottom you will have fuel running out into bilge.
Usual precautions apply when working around fuel so as not to blow up.
You can also drain fuel tank into 6 gallon poly gas cans, and pull tank out of boat to inspect.
If it's original may be in bad shape same for fuel fill and feed lines. With tank out can use it to have replica built locally. Will have to take it out anyway if it laeks.
