[flybouy]

Depending on the condition of the threads in the tank you could get a "pipe tap" and "chase" the threads by running the tap in and out. This will work if the threads are "rolled over" by "pulling" the threads back to the proper position. If the threads are actually "pulled out" then it's game over. If you can't find the tap you can try taking a black iron nipple of the correct size and "create" one. I've done this on occasion with decent results. Take iron pie and clamp it in a vise or flat on a table. Take a Dremel tool with a thin cut off wheel and cut 5 or 6 grooves perpendicular to the threads. Then use that nipple as a tap to clean up the threads.