How to remove a bulkhead when the threads are stuck tight

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This weekend I will be replacing a bulkhead that has a very slow leak.

Last time I replaced a bulkhead I could not loosen the threads to get the bulkhead off. The threads were welded tight together either by sand working its way between the threads or by salt creep evaporating and blocking up the threads.

I had to take a drill and drill through the outer plastic ring of the bulkhead to break the ring and then remove it, it took a long time and it put my tank at risk drilling right next to the bottom glass.

Does anybody have a better idea about how to loosen a stuck bulkhead?