Bulkhead leak - Need a fix!

[enlighten]

Let the larger bulkhead dry and re tightened but it comes loose quite easily when the pipe moves. Should I attempt to seal it from the bottom with aquarium sealant? Should I replace the bulkhead completely with a schedule 80? If I go the latter route, would it be worth to remove the ball valves completely? Tank is empty, so this is my chance to do plumbing right from how the previous person set it up. Any ideas welcome!

Drain pipe is 1.5" so i assume this is a 2" bulkhead. can someone confirm? return is 3/4"

 

[enlighten]

Duplicate post, idk who the admins are. Please ignore.