good job on the tee
once again, silicon is not the answer to anything especially a leaking bulkhead
pull the durso drain pipe and drain the overflow box...
take the bulkhead off and dry the area REALLY good... if you come up from the bottom with a napkin and run your finger around the ring you can dry it up and make sure there is nothing where the seal will seat, not even one grain of sand...
clean the bulkhead off and the gasket off really well, make sure NOTHING is ont he gasket
put the bulkhead in from the top (gasket on the wet side) and tighten the nut. make sure not to let the bulkhead spin on the inside so the gaket doesnt get kinked... most people say hand tight but I think hand tight plus about 1/4 to 1/2 turn with a channel lock works good. it should be sealed.. if not something may be wrong with the gasket