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I need to run a drain line for a sink through a multitude of joists. I could certainly cut 16" pieces of PVC pipe and use couplers to join, but, the numerous joints seems like an excess of places that failure could occur.

PVC pipe, with added plasticisers to make it flexible, behaves almost exactly like rigid PVC in terms of pressure rating, interior smoothness, etc. It can be solvent welded into regular PVC fittings. Would it be to code (2018 NSPC; I'm in NJ) to use a carefully supported run of flexible PVC to ensure slope is maintained in place of rigid PVC with numerous joints?

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Flexible drain lines are VERY prone to "double-trapping" themselves and failing to work. I don't know from a code POV but I'd guess not, and I know from experience that "draining things with hoses" can be fraught with peril - yes, I note that you said carefully supported.

In most cases by using slightly oversized holes and exploiting the slight flex of "rigid" pvc it is possible to get "longer than one joist bay" sections of pipe between joists. You can almost always get a two-joist bay section (i.e. 32" in this case) section in place just by angling it up and then rotating. Whether you can get more than that depends on the size of the pipe and the position of the holes relative to the bottom of the joists, unless you can get "end access" at one end to stick it in straight.

The other option is to run it below the joists.

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  • Sadly this is getting added to the very end of an existing drain run, so, I'm very close to the top of the drillable region of the joint already. Its a miracle I'm going to be able to slope it enough at all, but I definitely would have to go one bay at a time. – David Pfeffer Aug 4 '20 at 13:25
  • I don't know plumbing very well so I'm not posting this as an answer, but why not just notch the studs, put in the pipe and then nailers covering the notches? – George Anderson Aug 4 '20 at 14:05
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    Building fall down go boom - generally not a good thing. – Ecnerwal Aug 4 '20 at 14:15
  • @GeorgeAnderson The pipe is at the top of joists, not studs. :) I'd have to remove the floor above the joists to notch and lay in pipe. – David Pfeffer Aug 5 '20 at 14:33

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