The pipes are labelled "INERT REACTANT". Apparently that's not the oxymoron it appears to be.
Sounds exactly like something you'd find in a water purification installation...
(Supposedly, it becomes less inert when it enters the purification process. But it's very nice that it stays inert the rest of the time.)
I'm just glad they didn't spend a single second of the movie in those damn crawlways thay TNG/DS9/VOY keep going back to
The fact that one can't easily find those things on shooting locations should probably tell the film crews something. Although it's probably more an issue of only set-built crawlways being filmable, whereas some real ones exist as well but cannot accommodate a camera.