I just my first repark job on my garand. I didn't have a stainless steel tank, so tried a technique I heard about on
www.falfiles.com. I bought one of those long plastic storage tubs used for wrapping paper for like $8 - its about 48x6x8 - a bit bigger than needed and so required some extra solution. Anyway, I just heated up the solution in pots on the stove, placed the items to be parked in the "tank" and poured the solution in - trying not to pour it on the parts themselves. I heated the solution a bit on the high side - about 190F (bought a candy thermometer as mentioned above). I also kept some heated in "reserve" that I poured in about 10 minutes into the process to keep the heat up. The process finished and stayed hot enough to get the job done.
Some others have done a similar process, but used PVC tube they cut in half and capped the ends. That would probably be a bit more efficient in regards to the amount of solution you need.
You could use the black iron tanks, but the inside of the tanks will get parkerized themselves. Once they are completely parkerized, though, the process should for the most part stop. However, you would be wasting a portion of the solution parking the tank. I have heard that the solution will eventually eat through the iron tank, but shouldn't if store the solution in another container when done.
What you could probably do, if cost is a concern, is set up a double boiler system using the method outlined above along with your tanks. Just put plain water in the iron tank and suspend the plastic tub or PVC pipe in the water with the solution in the water. Heat the water in the tank, which should in turn heat the solution in the tub or PVC.
However, if you want to do it "right, in addition to Doubleought (the owner of
www.parkerizingtanks.com), another member at the falfiles by the name of Deltaten has offered SS tanks in the past for a bit cheaper. I'm not sure if he is going to continue to make them, though. IIRC, he needed one himself but ended up making a bunch and selling them, but I believe he did another batch after that as well.
In regards to the chemicals, I'd say just buy the pre-mixed from brownells. My first attempt was using a homemade mix from chemicals bought at home depot, etc. All the running around looking for brand X,Y,etc cleaner that contained phosphoric acid was basically a waste of time and money. Even when you finally find the proper cleaner that has the proper chemical, you have no idea what the concentration really is.
One bottle of the concentrated brownells zinc solution is enough to make 4 gallons of solution, and I believe is under $10. The manganese solution ends up being more expensive, as there is a higher concentrate:water ratio. Unless you are going to be doing this in volume, you likely won't see any cost savings in buying the chemicals from a chemical supply house and mixing the solution yourself. The single batch of the solution can be reused multiple times.
Many people seem to use the stovetop burners with good success. However, you are heating the solution unevenly, which may result in "hot spots" in the solution which in turn may result in an uneven finish. If you are going to do it this way, it may be best to give the solution a stir every once in a while. However, this is just my thinking logically - not anything from experience, being I just used the plastic tub method so far.
The "Links" section of parkerizingtanks.com should have lots of links to directions on the process itself.
Hope I covered mostly everything...
Rocko