Help with Waste Tank Plumbing

[tinbender]

I am in the process of replacing the dump valves and associated piping on a '78 Argosy Moho. I got the piping out of the tanks today and saying it was a challenge is an understatement. When I got the pieces of piping out of the tanks I could see some sort of goop?? on the ends as they came out of the tanks. Whatever it was worked well as there were no leaks at the tank connection.

Hopefully will have all my parts rounded up in a couple days so would like to know if someone can tell me what I need to use to take the place of whatever that stuff was, on the end of the pipe that goes into the tank???

Any help appreciated.
Thanks much, tb