Hey Lloyd, how do I do the "Electrolysis" thing? I wouldn't mind trying it out on this tank while I'm waiting for the replacement to arrive? Cheers, Terry. 
Sure Terry,
It's pretty simple but slow.
Get yourself some Arm & Hammer Super Washing Soda (sodium carbonate). Mix this in enough water to fill the tank at a rate of about a tablespoon per gallon. The carbon makes the water conductive and more soda will increase the current. Remember this, if you need to get some higher current action on the battery charger you select.
Make yourself some sacrificial electrodes to stick into the tank opening. I used old wire coat hangers (wire brush off any paint to bare metal) folded back on itself so they would fit through the filler opening. But, if you have stainless steel that would be better from a how long will it last point of view. You will want as much surface area for the electrode ans you can possibly get into the tank without it touching any part of the tank. I used an old rattle can plastic top and punched a hole in it to insert the wire through. Then bent the coat hanger wire so it would suspend in the water inside the tank, without touching the sides.
Connect a battery charger; the negative lead goes to the tank metal, the positive lead goes to the electrode. Polarity is important as it determines where the rust migrates from and to.
If your charger is adjustable, set for about 10 AMPs. My charger was only 6 Amp capable ( I bought it in 1963!). It worked, but slowly and I had to increase the Soda density to keep the current up, since it doesn't put out a very high voltage.
As the electrode collects rust, the current will go down (Nice to have an ammeter on the charger) and the lower the current the slower the removal action. So, after a few hours, disconnect the charger, withdraw the electrode and clean it off. I used a wire wheel. Re-insert the electrode and resume the derusting. Repeat until until the tank is once again bare steel. If your electrode falls apart during cleaning, replace it. I used about 10-15 coat hangers over a couple of weeks.
As the tank gets cleaner, the current will go down, to. Don't change your charger current setting to increase the current beyond the initial setting.
A couple of warnings.
The electrolysis action also liberates both Oxygen and Hydrogen from the water, these are the bubbles you'll see inside the tank during the process. Make sure this is vented outside, unless you want your very own Hindenburg demonstration in your garage.
Also, the process lowers the water (electrolyte) levels inside the tank, and the space then collects these gases. A spark from your charger clamps, will set this off. Bang! It sent my 1/8 brick I was using to hold the plastic cap/electrode positioner straight into the air about 6 feet and bulged the tank, too!
That's about it. What's nice about this process, is that it doesn't remove ANY steel, that an acid etch would. Just the rust.
When it's over, and the solution drained (the solution looks nasty but will still work fine) I used a couple alcohol flushes to extract any remaining water from the tank, (to prevent flash rusting again), did a blow dry using a small fan, and didn't get any more rust.
That's as far as I got with my test tank, as all the paint blisters started weeping when the rust was removed and the remaining metal was, and still is, quite thin. I'm going to try and braze them up one day, if I can't find a good tank for a reasonable cost.
Feel free to ask questions if I didn't explain it clearly.
Cheers,
