New Disposal to Old Wall Drain


Old 05-01-05, 12:18 PM
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New Disposal to Old Wall Drain

This is a basic question and I hope not too stupid, it's also similar to an earlier post I just read asking about the height of a wall drain.

I'm remodeling a kitchen in an old house, installed new double sink with disposal, trying to have everything drain into the old wall drain.

Height seems to be the main issue!

Even I realize that water drains downhill, so I'm assuming that all the vertical and horizontal runs must occur higher than the final wall drain (??????)

If so, does this also apply to the bottom (lowest bend) of the P-trap?
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Old 05-01-05, 02:16 PM
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Normal plumbing codes dictate 1/8 to 1/4" per foot slope for drainage, depending on local code. Your sink drain is PROBABLY within 4" plus or minus of being a foot from the wall. This is not a lot of slope if you eyeball it. You are basically trying to keep water flowing towards the main drain. Code is from one end of the horizontal line to the other. Trap is not included as far as a LOW point. You can run your line from the wall out and install the trap (making sure of the slope, and then buy the appropriate length tailpiece to go from the sink drain down to the trap. Hope this helps explain it. Good luck with your project.
Old 05-02-05, 03:25 AM
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Be sure to check things out before you go too far. I did something similar a few years ago in an old house. I ended up having to redo the wall drain and vent pipe because the outlet of the disposal turned out to be 3 or 4 inches below the drain hole in the wall. Trust me, a disposal isn't a very good pump!

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