Thank you for your kind words.
However, our resident crosswords whiz is Dutchy.
Unfortunately, we don't have any Lovatts, Mega Stikers and so on here in Paris.
As so, I only can give guesses from the clues and the letters you have already.
As for your question, I would guess:
Pipe through which wastewater (sewage, stormwater, industrial effluent, etc) is discharged to a receiving body of water.