I started cleaning the inside of the tank. Once clean, I'll take care of the exterior.
My process, so far:
1. Dove and hose blast, twice to get rid of loose crap. Dump and dry.
2. 1 gallon vinegar and lots of swishing. I put a scotch brite pad on the end of a stick and spent a few hours scrubbing all areas I could reach. This scrubbing with the one gallon vinegar puddle was very effective, I thought. Not all areas could be reached, of course. Let vinegar sit for a day. Dump.
3. Then the big guns: Muriatic Acid approx 15% concentration, one gallon. Swish around. (Tip: I used rubber expandable plugs that are used to pressure test plumbing to minimize splashing. I left the small vapor and return barbs open to allow the whole tank to vent.) I let it sit for no more than an hour, turning and swishing every few minutes, until everything was squeaky clean.
4. Dump the acid in a bucket and funnel it back into a storage container for reuse.
5. Hose out the tank, dump the water in a bucket, neutralize the bucket water (not much baking soda was needed), and while the tank was still dripping wet inside, added half gallon of phosphoric acid. Let it sit for an hour, swishing occasionally.
6. Dump, dilute the remaining acid with water, add baking soda until fizzing stops. Swish and dump.
7. Hair dryer on high heat and air until bone dry, maybe an hour. (It was too hot to pick up with bare hands.)
There is some flash rust, and I'll probably do another round of phosphoric acid tomorrow. I'm happy with the results - a lot better than "as received".
Last edited by doctorb; 08-29-2019 at 03:12 PM.