Homebuilt ROVs Forum

I am trying to build an underwater rov with 4 inch PVC. I am stuck with leak proofing my end cap. I am attaching an Image of what I have. It is a threaded connection. I am looking for some ideas to prevent water leaks. I see that the stinger model shown in this site uses similar cap.
http://www.homebuiltrovs.com/stinger.html
Also the pressure champer also seem to use this end cap. http://www.homebuiltrovs.com/pressurechamber.html

Plumbers tape. Put quite a bit on, the more the merrier. And then make sure it's tightened all they way down.