Draining/venting a dishwasher, without a sink


Old 11-22-13, 12:08 PM
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Draining/venting a dishwasher, without a sink

I want to put in a dishwasher in an island where's the no sink. I've been reading about air gaps but if I don't have a sink or no outside wall nearby, an air gap seems wrong. I plan on running a 2 inch pvc pipe from the basement straight up into the cabinet beside the dishwasher so the top of the pvc pipe will be near the top of the dishwasher. I'll put a trap in too. I'll do a high loop with the dishwasher hose, and then connect it to the pvc pipe. The big question is, am I done? or do I still need something like an air gap or a AAV?
Old 11-22-13, 12:16 PM
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You will need a AAV. Also discharge the DW hose into a stand pipe with trap. Just like a washing machine. This provides the air gap.
Old 11-22-13, 03:24 PM
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Here some ways you may be able to do it --- depending on local code.

Attached pictures showing a sink --- just substitue the sink with the dishwasher.

First way -- Island vent method

The "island vent" is the most accepted way to vent an island sink and should be permitted by inspectors in most areas --- at least it is up here. The basic principle is simple, the vent comes from below the floor and is tied into the drain pipe from the top, this allows the waste water to drain normally while fresh air is brought in to protect the trap.

Install horizontal drains with a downward grade of 1/4" per foot.
The vent can be taken to a nearby wall or also run to the stack and tied in above the drain.
Install clean out fittings in accessible places.
Bring the loop as high to the counter top as possible and it should be one pipe size larger than the drain.

Second -- Through the floor method

A new provision was made in the 2005 Canadian Plumbing Code to allow for fixtures; such as island sinks, to be vented normally. The change was to allow for the fixture outlet pipe to be taken through the floor and then the trap arm would be connected to a vent.

Third -- Air admittance valve island vent method

Another and much easier method of venting an island sink is to install an "air admittance valve" (AAV), however this may not be an acceptable solution in many area's. Always consult your local authority for the latest code requirements. An AAV will allow air to be sucked in whenever the drain pipe has a negative pressure, but will remain closed under normal conditions to protect the home from sewer gasses. These devices are mechanical and all things mechanical are destined to fail, making them the least desirable of the two venting methods --- personally , I don't like them -- but that's me.
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Old 11-26-13, 11:02 AM
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Thank you for the replies. Very helpful. I wasn't aware this would be so complicated without a sink. With the island vent method, why is the vent connected to the drain pipe in 2 spots? is that neccessary?

With the through the floor method. Can I vent the trap arm anywhere along the arm? I would think it would have to be vented close to the trap.
And why would there be a maximum trap arm length. As long as it's slightly sloped, shouldn't longer be ok?

I might be stuck using the aav method unless I want to remodel my whole kitchen.

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