help(bulk head)
 

I have a brand new tank Im trying to plumb it but the bulk head for the return pipe keeps leaking I just bought a new bulk head tried that and it made no difference.I have the bulk head faceing to the roof and the nut for the bulk head underneath.Do you have to use a tool to tighten it cause Ive installed bulk heads before and never had a problem.

You may have a small chip in the glass so that the rubber gasket does not form a seal with the glass no matter how hard you tighten the bulkhead. What you could do is run a bead of silicone around the bulkhead (on the flange side) and tighten it down. Of course you would have to leave the silicone to dry for a few hours.

Dont overtighten

The rubber seal is on the water side of the glass right? Make sure you dry the area and bulkhead thoroughly before install.

As suggested, don't over tighten and use silicone to seal it if you have to.