Our Plumber quit, so I got this. In a lab they have a Blue Catch basin under the sink, in case something goes down the drain that wasn't supposed too. There is a Blue Nylon, 2" FPT fitting welded to the Basin. Threaded into that is a Blue PVC nipple. I can't stop it from leaking with Teflon tape. What plastic safe Sealant can I use, on what probably is a stretched Nylon fitting?