For a vat or tank, get some 16 ga. hot rolled or even cold finished steel and just bend up what ever tank size you need. Do consider the shape or size of burner you have. Make sure any welds are tight and will not leak. Put bent up 16 ga. handles on each end but NEVER try to pick up a hot tank, only use the handles to move it after things cool down.
The polish will determine the final finish. For cleaning prior to putting the parts in the salts tank, use a pot ( not aluminum if you can help it ) or just make up another tank and use Tide soap in boiling water and scrub everything with a good long bristled scrub brush. There is no need to rinse but if there are areas that might hold this water mixture, be vary careful how you set it in the salts. These small water pockets can cause one heck of a explosion. I use about 1/4 to 1/3 cup Tide to about 5 gallons of water.
I actually use 4 tanks when up and running. One for the hot salts, one for the cleaning tank , one with hot clean boiling water and one for clear cold water. Sometimes and with some metals the salts just don't want to "bite". I carefully take the parts out of the hot salts and quickly put them in the cold water. This creates a "shocking" effect and will sometimes get things cooking. Put some 4 O steel wool in a 3 pound coffee can, cover with water and boil it, pour off the top water and recover and boil again. This removes the packing oil from the wool. If you notice spots or a red or green rust forming on your parts, remove from the salts bath, plunge in the cold water and rub off the rust with the cleaned steel wool and rinse in the hot water tank then back in the salts.
I wear gauntlet rubber gloves, a rubber apron and a full face shield. Hot and itchy but I have seen others get badly burned from this process and thats one club I don't want to join.