[DrHank]

I'm not absolutely sure but it looks as though it may have originally snapper in place. I don't think that the flange was intended to allow the part to turn. On closer look, the part appears to be black plastic and not acrylic. Weld on is used to cement clear (or other) acrylic. If it is just black plastic, I'd use Oatley All purpose cement. You can find it in the plumbing section of any hardware store, Lowes or Home Depot. It's going to cost you though. At least $3 - $4.

I don't much care for duct tape in salt water (or any water). As far as baffles are concerned, if the tank is glass, the baffles should be glass. If the tank is acryilc, use acrylic (plexiglass) baffles. That would be where you would want Weld on (acrylic to acrylic). If glass use aquarium sealent or GE Silicone I (don't use anything that has a mold inhibitor).