So that's what that stuff is. All I know is that it kinda sucks.
To drain my water heater on my 1993 TT I have a gray line that hangs down underneath the TT. It had a female end on it and you would screw a plug into it during the summer to keep pressure in the system. Suppose to be some sort of cone shaped o-ring in there. I can't seem to find the right ones of those.
This year the female end broke. I was able to use thread a 3/8 bolt with Teflon tape on it up into the line. By golly that has been working well.
I don't know what I am going to do next year though.