Can a dishwasher drain hose be connected after the sink trap (to the trap arm)?
Saturday, October 5, 2019
No, the dishwasher discharge must be connected before the trap. According to the Florida Plumbing Code it must "discharge into a wye branch fitting on the tailpiece of the kitchen sink or the dishwasher connection of a food waste disposer.” The International Plumbing Code citation is similar.
There is also an alternate method allowed, of an indirect drain with an air gap, which we have never seen at a built-in dishwasher installation. So the example shown below, where the discharge line is connected after the trap at the trap arm, is not allowed.
The reason that connecting the discharge after the sink trap is prohibited is that this wrong configuration is behind the U-shaped plug of water that keeps stinky, and sometimes lethal, sewer gases collecting in the dishwasher.
And here are two examples of the correct way to do it.
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