As this old tank is not available, here were the steps to recoat the tank:
Using proper safety equipment (Respirator, Gloves, Long clothing, eye protection, head covering etc). VERY FLAMMABLE - Do this outside and away from animals, sparks, light, humans, etc
1) Remove tank, sending unit and tube
2) Drain fuel to suitable container with rust
3) bang with rubber mallet all over sides and top
4) Pressure wash to remove more rust
(Several times)
5) add half gallon Muratic acid (HCL)
6) seal hole with good duct tape
7) slosh around (SAFETY EQUIPMENT VERY IMPORTANT), let sit for 30 min, drain to plastic barrel
8) Mix 1lb baking soda with 5 gal water.
9) Add in 1 gal batches, seal and slosh. dump to same barrel as above watch for foaming in tank. NOTE: When you dump baking soda in the acid it creates toxic gas!!! Wear respirator!!! also LOTS OF FOAM> Do this slowly.
10) Repeat 6 times or so, watching for reaction foaming in tank.
11) When no more reaction, pressure wash tank again - allow to dry a little - but not all the way.
12) Use 1 pint MEK or equivalent in tank and seal/slosh again. Dump to another tub to evaporate
13) Same again - 1 pint MEK.
14) As my sloshing compound was MEK based you can add it right after dumping second pint to evap tub.
15) Add compound and seal/slosh. Slowly move the tank from side to side allowing compound to coat walls. (about 1 quart of compound for this 24 gal tank)
16) I didn't have to remove any afterwards as the tank took the whole quart to coat it.
NOW> the acid barrel is still nasty. Add roughly 5 boxes of baking soda per half gallon to neutralize. Do this VERY SLOWLY. You will have a massive reaction every time you add baking soda. add till no more fizz. (Takes about an hour or more to complete this step).
Call your local city to then dispose of this material. DO NOT DUMP IT.
This job is better handled by pro's that do it every day. However if you feel you need to tackle it then there are some steps. More advice is on the can for the sloshing compound and on line. Different acids use more or less base so read about that.
