Tailings pond now empties without pump

[fvandrog]

I assume that it is not surprising considering the fluid changes, but I was not sure whether it is desired and/or easy to fix.

Tailingponds are now part of the open fluid network, and levels are (proportionally) equivalent. That means it empties automagically when there's a need for the fluid. Nicely compensates for the absence of valves, but might be OP.

(Anyway, I know that I am a bad PY player if I use/need Tailingponds at all).