Oh, I got it a bit wrong then, this way it is ok...as a mechanic
You basically used the water physics they have in the game and played around the pollution problem that way...nice find lol, it is so simple, yet so elegant. I will certainly not use it, but I appreciate what you did, you win teh internetz today!
Next thing, they introduce not only water pump/drain volume but pipe volume too, so you will have to construct miles of pipes in order to fit all the poo in
Edit:
All we need it terraforming tools (there is a mod for that I think), you dig a huge hole and pump all the sewage there. Poor China though! xD