In most kitchens I've seen, the dishwasher is pretty close to the sink. In fact the sink and the dishwasher often share a shut-off valve. So if you run the water at the sink until it's hot, then start the dishwasher, it will get hot water.

Problem is, that most dishwashers have a prewash and a main wash. By the time the prewash is finished and the main wash starts, the water in the supply line will have cooled off quite a bit.

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doubled112 9 hours ago | parent [-]

Not just the shut off. My dishwasher's drain hose goes up into the sink's drain plumbing much higher than I would have thought.

This almost made a mess when the sink was clogged and the dishwasher tried to pump the water out but had nowhere to go.

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tguvot 8 hours ago | parent [-]

You can install airgap for this. In usa building code mandates it on multiple states

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olyjohn 8 hours ago | parent [-]

Is that the point of the air gap? I can't even get a straight answer from plumbers on what it's for. I don't see how that could possibly help with a clogged drain, just seems like a secondary point for the drain water to come out.

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SchemaLoad 7 hours ago | parent | next [-]

I'm fairly sure the point of air gaps on drainage is to prevent sewerage water from backing up in to appliances if the sewerage line is blocked. It will instead spill on the floor where it will be more easily noticed and cleaned.

	▲	db48x an hour ago \| parent \| next [-]
		That is exactly why they are required in restaurants. You wouldn’t want the sewage to back up into a sink where food or dishes might be.
	▲	throwaway173738 4 hours ago \| parent \| prev [-]
		That’s exactly what it’s for. If you block the sink drain and fill it with water, you can have water flow down the dishwasher drain hose and into the sump in the dishwasher. If that happens during the rinse cycle you’re rinsing with grey water.

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bcoates 6 hours ago | parent | prev [-]

Pumped out water has to go somewhere . With the airgap, it will either back out your garbage disposal or pour out your airgap into the sink basin, depending on the location of the blockage.

The airgap causes the pump to be physically incapable of backfeeding the drinking water supply with dishwasher waste

	▲	tguvot 5 hours ago \| parent [-]
		iirc its less about contaminating drinking water (there is a valve and pump to get through. rather tricky) and more about waste getting into dishwasher during cycle and you getting contaminated dishes. my wife once decided to dump into garbage disposal a bunch of uncooked broccoli at once. it clogged garbage disposal and drain. when i tried to unclog it with plunger it backed into dishwasher (was hooked directly to garbage disposal bypassing airgap). took me hour to get everything out of dishwasher.