UPC reads:

'414.3 Drainage Connection. Domestic dishwashing
machines shall discharge indirectly through an air gap fitting
in accordance with Section 807.3 into a waste receptor, a wye
branch fitting on the tailpiece of a kitchen sink, or dishwasher
connection of a food waste disposer.'

Does tailpiece mean vertical? Can one plumb a dishwasher to a horizontal tailpiece of a kitchen sink? Does a dishwasher need its own trap if one can route the drainage hose so as to form a p-trap?

More code:

'419.2 Drainage Connection. Approved wye or other
directional-type branch fittings shall be installed in continu-
ous wastes connecting or receiving the discharge from a food
waste disposer. No dishwasher drain shall be connected to a
sink tailpiece, continuous waste, or trap on the discharge side
of a food waste disposer.'

This means I can't install a dishwasher drain directly after a disposal. But what if it's a 2-bottom sink and the dishwasher is installed on the other sink's tail piece, which the disposal's has joined?

I'd like to explain WHY one needs an air gap in the first place.

ALL mechanic check valves WILL fail. It may be today or 50 years from now however we recognize all mechanical check valves will fail.

WHEN the dishwasher check valve fails the water in the discharge line will silently go back into the dishwasher or connected drain.

Any water in the disposer or connected drain will then naturally by gravity get pulled/sucked back into dishwasher which at the end of the last dishwasher cycle can then contaminate all that is in the dishwasher .. bringing bacteria, etc back into the bottom of the dishwasher.

The homeowner won't be aware of the contamination.

Why I'm sharing this is for us to recognize how it all works and why having an air gap is so important.

Whether after the airgap the drain is connected to a verical or horizontal line doesn't matter as long as after the connection to the drain/dishwasher there is a ptrap and then a proper/legal vent.

Doesn't a high loop on the drain hose accomplish the same thing as an air gap?



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Theoretically speaking a high loop can be even more than 10 feet high and still be able to syphon and so in my mind where I am at as far as "plumbers protect the health of our nation" is that I will never use or recommend a high loop.

If one doesn't want to or it's not possible to install a standard air gap above on the sink or counter there are various other designs of air gaps made such as designed for water softeners that leave an open physical space before going into a standpipe with a ptrap below it. I have seen many in the Denver area.

Thanks for your answer. I didn't ask about the air gap, but a dishwasher's drain connection.

After the air gap one can attach that discharge hose to a verical or a horizontal drain pipe .... a tailpiece is also condidered a drain pipe.

Thanks.



Edited 1 times.

Air gaps are not required by code in Toronto. I have been in thousands of kitchens in Toronto and can count on the fingers of one hand the number of air gaps I have come across.