Leaking Overflow Bulkhead

You could also buy a longer threaded pvc pipe and thread it from the bottom up. Have your wife hold it in place. Then use a clamp or lock vise on the nut and remove it. The longer your clamp on the nut, the more leverage you will have to twist it off easier.

Spraying it with some vinegar will also help to remove the salt creep sealing it together.

Good luck