ok, project continues. Used inflatable dinghy foot pump to pressurize the fuel tank to 3psi. It held pressure for 10 minutes. Now I will use pressure washer to clean out tank through the small fuel gauge sending unit hole. Then I will use a shop vac to pump out all the water and allow the tank to dry. Hopefully that will do it!! What a pain this is.
First, it is a waste of time to test for leaks
before cleaning the tank. The dirt often clogs the holes. You will need to test it again after cleaning, since the cleaning sometimes makes holes.
When you re-test, cover it with a soapy water bubble mix to look for pin holes (just a little hand dish washing soap in water). That pressure is way too low to find leaks on it's own (but you don't want to use more pressure).
(I'm an API licensed tank inspector. I've inspected thousands, up to 10,000,000 gallons.)