Type of bulkhead (wet side + dry side) - threaded + threaded; threaded + slip or slip

[WarDog]

Something is not right here. Either your bulkhead threads or your MPT threads are hooped, or are not MPT at all, but you have used two and are seeing the same results. Hmmm. I have 2 suggestions. 1) Teflon goes clockwise around the threads, so as it doesn't unwind as you tighten. 2) You may want to use wrenches to assist in tightening, however go slow and careful not to split female threads. If all else fails get yourself some slip slip bulkheads. Hope this helps.