Myself and others have had decent results cleaning an old tank that is otherwise in good metal condition
I drain them out well
Put in about a gallon of clean gravel
Lots of water and some detergent of choice
Shake it around a lot
Rinse and rinse and rinse
Stick a vacuum discharge hose in it for a few hours
I’ve been running one truck that got that treatment well onto 10 years now
Takes a long time to build up line clogging levels of junk
I didn’t even put a filter anywhere in the system which I really should one of these days
Ideally under cab where the tank line goes to the steel line on the frame rail I think would be a good place.
-s
