"Leftovers" in between shutoff valve and cap after dumping tanks?

[Shorty Cox]

I did what Jason did. Put a twist on valve at the end of the drain. Stops the problem.

[GiddiYup]

Appreciate all the input.
Cheers!

[TeamFoxy]

We just stayed for a week at a state park and used a tote tank to dump into. No leftovers drained out when we opened the cap. We stopped at the dump station on the way out and sure enough, there was liquid in the cap. This confirms my feeling that our problem has nothing to do with the valves and everything to do with the pitch of the pipe between the valves and the outlet.