I am working on installing a new dishwasher. The location of the install is also the location of an old washing machine (and not directly adjacent to the sink) so I was hoping to use the old dishwasher standpipe for the drain (1.5" pvc pipe). The top of the standpipe is only a few inches above floor level and the p-trap (2") is about 35" below floor level in the basement (photo below). I know this is not necessarily standard installation for dishwasher drainage, but can it be done this way? Will I need to add an AAV to the line? And where would I add the AAV? Possibly replace the current trap with something like this?

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2 Answers 2


Yes you can put a dishwasher here, yes you need a vent so the trap doesn't get sucked empty. Something like the trap kit that you linked would work, IE a trap and an AAV. I'm not sure if that specific one should be used. Usually standpipes, for laundry machines without basins are bigger than the 1-1/2" you have there. But it's normal for dishwashers to drain into 1-1/2" traps without overflowing into the sink above, so perhaps it will work.

There are practical reasons dishwashers are plumbed into sink drains: a sink is very useful near a dishwasher. Are you not going to have one nearby?

  • do you have any recommendations for another AAV that might be better suited for the situation? Oct 15, 2023 at 0:10
  • 1
    Again, your linked one might be ok but if you search for "2 inch AAV" then glue up a trap and AAV similar to the one in your link using 2 inch parts, that might be an improvement. I say "might" because it may not be necessary, the 1.5" might be ok. Either way you can get rid of the existing trap and tie into the 3 inch pipe.
    – jay613
    Oct 15, 2023 at 0:42
  • thanks very much for the info. thoughts on the 3/4" dishwasher drain meeting the top of the 1.5" stand pipe: should that be sealed, or left open, or it doesn't matter? Oct 15, 2023 at 1:23
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    Hooked over the top and held firmly to it. Not shoved in too much and not sealed. Like a laundry drain. Keep an eye on it for the first couple of loads.
    – jay613
    Oct 15, 2023 at 3:35

The dishwasher hose is 3/4 inch rubber tube.

If you insert it into 1.5 inch stand pipe and DO not seal it (leave the air gap) it will provide enough air vent.

Not so long ago and even today, there was a simple air vent mounted on counter top

  • The purpose of the AAV is to avoid precisely what you describe here, by admitting air after the trap. It's needed.
    – jay613
    Oct 14, 2023 at 23:19

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