What is the best way, to clean out an old fuel tank, if possible without removal, but I can take it out if better. And what brand of solvent is best.

Thanks

The tank really needs to come out for cleaning.

I have had good luck with the Eastwood 3 step kit for "at home" cleaning. It used strong detergent, muriatic acid and acetone for cleaning duties and then a sealer.

If the tank is readily available as a re-pop it may be easier (and cheaper including time) to just change it. If it is a rare and expensive tank, different story.

I think your pretty much gonna have to pull it cuz there's no real way to get in there to agitate things. if you have a shop that hot tanks blocks that will work tho the EPA is making them harder to come by. Otherwise going to the car wash & using the wand & I would think their soap is pretty stout (maybe maybe not). To ans your Q I think any solvent would suffice. If it is in bad shape I would suggest a new tank, Spectra from Canada is good (I used one & good reports from others also) & it gives you the opportunity to solder in a drain bung and one for the fuel inlet on the front wall near the bottom. You can keep the sending unit as is for that function

You might also check with an old school radiator shop...if you have any around you. They might boil out the tank as well. (One around here used to ages ago at least)

I've always pulled them and had them hot tanked. Sometimes takes a little looking to find a place that still does it...

I used POR15s kit in my 65s.That was in 98 or so.It was totally nasty and I thought it was junk.Pulled it followed the directions to the letter.Let the sealer set in the tank as instructed drained like it said and thenlet it sit for a day in the sun. Still looks better than new today.Rocky