Dishwasher draining

[kactuskid]

What is the proper way to drain a dishwasher if the drain is installed down through the floor rather than sideways under the kitchen sink. Say if the dishwasher is on a different wall than the sink and the drain hose is looped up behind the dishwasher to prevent the water from draining out while it's being used. Like the last picture on this link:

http://web.appliance411.com/faq/washer-drain.shtml

Then how is this hose extended downwards, since now it's really short, and how is it tapped into the main drain system. Is it possible to tap a 2" branch drain line using a solid connection. Seems to me it would need to maintain an airgap of sorts, like a washers standpipe. Just curious, thanks.

[LazyPup]

The Codes all require that Dishwashers must be connected by means of an indirect waste, however the manner of achieving such a drain vary greatly from one code to the other.

In this case the dishwasher is installed away from the Kitchen sink so the conventional connection to the garbage disposal or sink tailpiece is out of the question.

Under the Uniform Plumbing Code all dishwashers are required to have an Air Gap fitting installed above the countertop. The drain line must then run to the air gap fitting and a second line run from the air gap fitting to the final point of connection to the drain system.

The International Residential Code does not require the air gap fitting, however many local codes have been ammended to require it.

The International Residential Code does require that the drain line be run up as high as possible under the countertop and secured in place, then dropped back down to the point of final connection. Also, in order to acheive an indirect waste there must be some means of creating an air gap in the drain line.

Both codes will allow the use of a standpipe and trap assembly similar to those used for laundry washing machines.

You could make a lateral waste arm from an existing drain, attach a trap and add a vertical stub up to create the standpipe however you must meet all the specifications for venting a waste arm.

While you could run the dishwasher hose through the floor in the manner shown in the drawing on the website you supplied, I personally would be very hesitant to do so. If the point of discharge of the dishwasher drain line is below the floor, it then creates a syphon loop in the dishwasher drain. In a worst case scenario it could cause the water in the dishwasher to syphon out of the machine prematurely during the run cycle.

I would prefer to run an 1 1/2 drain line from the existing drain in the basement or subfloor location, then stub that line up through the floor to create a standpipe in the immediate vicinity of the dishwasher.

Under the International Residential Code the Trap could be located below the floor and the Standpipe must extend a minimum of 18" and a maximum of 42" above the trap.

Under the Uniform Plumbing Code the Trap may not be below the floor. It must be located a minimum of 6" above the floor and the standpipe inlet must be a minimum of 18" and a maximum of 30" above the trap.

Under the IRC the maximum horizontal distance an 1 1/2 waste arm may run without an auxillary vent is 6'. The UPC limits an 1 1/2 waste arm to 3'-6".

If you are under the IRC and if your horizontal run is greater than 6' you could effect a suitable auxillary vent by installing an air inlet valve (Studor Vent) on the waste arm.

The Uniform Plumbing code limits the use of Air Inlet Valves to one per structure and only with the written approval of the local inspecting authority. The option would be to install an island vent.

If your horizontal run is greater than the limits listed above please repost letting me know which code is in effect in your locality and I will prepare a drawing with the specifications and dimensions.

[kactuskid]

Thanks alot LazyPup for all the great info. I agree, the best way would be to run a standpipe up behind the dishwasher. Excellent advice. Again thanks.