Good idea to find out where the leak is coming from.
My limited experience:
1. Tighten too much, and crack, bulkhead is broken, throw away and try a new one.
I got advice: clean around hole, clean gasket, and make sure it is absolutely flat. Gasket on inside of tank, put screw shaped thing thru it, and thread nut shaped thing on outside of tank, finger tight, and then maybe a little more, 1/4 turn.
Once I took the nut off a full tank and the pressure of the water on the screw kept gasket tight and the thing from leaking. Amazing.
The point is the seal of the gasket is realy important.
2. Once I had the gasket and the nut on correctly, and I was screwing in a connector. It leaked a little, so I tightened it and crack, it leaked more now. It was a crack in the thread part that extends out of the tank , so I drained the sump, removed the bulkhead, used some superglue to glue the crack, carefully, and when I reassembled it, to my surprise, it worked beautifully.
FWIW,
Kathy