Dishwasher Standpipe

sorethumbsMarch 14, 2011

I need some help guys. I'm going to be installing a dishwasher standpipe in a sink base cabinet. There will be a 2" riser comming up into the cabinet from the basement that will service a double bowl kitchen sink and the dishwasher standpipe. I'll tee off the riser for the standpipe below the tee for the sink. venting will be achived by an AAV.

My question is two-fold.

1)can I down-size the diswasher trap and standpipe to 1.5"?

2)can I use slip-joint fittings for the dishwasher stanpipe and trap?

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Your setup sounds overly complicated to me.
Usually, the DW drain line is connected to the disposal. If there is no disposal, they make a tailpiece that has a 3/4" nipple for the DW drain connection.

    Bookmark   March 14, 2011 at 5:23PM
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dishwasher standpipe is one way to go, and I think I'm the one who has mentioned it the most often. As mentioned above, there is usually a reason why. Good to know this first. Post if if you know why you are going this route instead of the simpler route.

Then, another route is the indirect drain, still on the same P trap as the sink drain.

Then, the most complicated is the AAV and separate trap. if you need to do it this way, say why, and post whether your plumbing code is based on Uniform or International. Even once you do get back with all this information, please understand that local AHJ can modify any clause about slip joints and 1.5" versus 2" sizing. So, you may be best off if you place a call and ask. A forum is good for some things but not for others.


    Bookmark   March 15, 2011 at 12:25AM
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Well if you need backround info here you go - What i'm doing is trying to fix a massivly messed-up situation in my own home. The home was built in an unzoned rural township and the plumbing was done by the guy who built the house. Inspector??? No inspector. Township did not contract with or hire one - no inspection needed or even possible.

Currently there is no venting on this branch. The exterior wall is buttoned-up and finished, cabinets are installed, and all plumbing is exposed in the sink base cabinet. There is no disposer - not a good idea on private septic. And remarkibly there is no problem with trap siphoning.

I have a nipple on one of the sink tailpieces currently. The DW is conected to that. There is no air-gap. I thought that this situation was not acceptable and did not qualify as an air gap. I don't like this set-up anyway.

One of you guys mentioned that a standpipe is difficult, really? seem pretty straight forward to me.

Can I down size the diswasher p-trap and stand pipe to 1.5"? Does the dishwasher p-trap need to be solvent welded or is there a slip-joint or other type of removable p-trap that would work (for future cleaning)? Thanks!

    Bookmark   March 15, 2011 at 10:01AM
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I have seen sj and approved too in situations like this one. I have seen 1.5" too, approved of course. Nothing I've said guarantees it's OK in your locality.

What you have is either a branch, or a trap arm (with no vent), and an arm can normally be without a vent. With only one P trap, you can have an arm without a vent, if the distance is less than a certain amount and if it's all on the horizontal plane with the 1/4"-per-foot slope. More and more description will be needed to know if what you have is ok by code. For maximum distances you need to know if your code is UPC or IPC based.
A standpipe on the same trap is just the same thing as the small Tee. Do you want to have two traps? Is is because you think you need two?

    Bookmark   March 15, 2011 at 5:55PM
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Is this to code?: A horizontal 2" branch extending 10' accross a basement ceiling. At the end of this branch would be a ell (not a long sweep, wye & 45, nor combo) pointing vertical. A vertical riser extends from said ell into the sink base cabinet above. Another ell in the cabinet terminates into a trap adapter fitting. The p-trap assembly from the sink terminates in said trap adaptor. Trap arm distance is approx 12". Also the 10' 2" horz. branch would not be supported and over time sagged, lost pitch, collected debris, and caused sink to drain very, very slowly. The p-trap assembly would be the only thing supporting the horz. branch and due to weight of the sagging pipe the SJ fittings on the p-trap assemby begin to fail. Like I said a messed-up situation and NO vent.

    Bookmark   March 16, 2011 at 9:25AM
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BTW - What does this mean?:

(quote davidro1) "A standpipe on the same trap is just the same thing as the small Tee" (end quote)

A standpipe would have its own trap.

    Bookmark   March 16, 2011 at 9:46AM
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A big pipe on the same trap is just the same thing as the small Tee (a small pipe). Eliminate the word standpipe and use the word pipe. This is what I meant. The reason I now rewrite it as �pipe� is because it appears that a standpipe must by definition have a trap, according to what you think a standpipe is by definition.

    Bookmark   March 18, 2011 at 4:31PM
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