Plumbers: Term for a Specific Drain...

I’m seeking a term for a drain found in commercial use where one pipe (of small diameter) drips into a larger pipe without use of a physical connection. I want to say it is called something like a weep pan, for a WAG?

Maybe my WAG is all wet! But, such a drain does exist…what is the correct term for this?


  • Jinx

You mean…no plumber has come across this? As I recall, related to this, there is a type of floor drain which is like a countersunk box. You might see this in a grocery store tucked under/near a refrigerator or freezer case to catch condensate. Does somem plumber know what this is called???


  • Jinx

I belive what you are talking about an air gap fitting, something like this (sorry, that was the best picture I could find, the same site has some good information about backflow prevention though.)

Plumbing code varies but normally anytime the water supply can physically contact the waste water some sort of device is required to prevent waste water from being ‘sucked’ into the water supply line in the event of a severe water pressure drop in the supply line. There are various backflow prevention devices to do this but a an ‘air gap’ is probably the best and most reliable.

A normal bathroom sink has an air gap because the sink will overflow before it reaches the spout, therefore there is no connetion between the water supply and waste water. On the other hand an outdoor hose can easily be placed into a bucket and contaminate the water supply in the event of a vacuum in the water supply, therefore in most places outdoor faucets are required to have a built in backflow prevention device.

I would guess in the case of a grocery store freezer there is probably a hose in the freezer for cleaning purposes or some sort of built in spray, the airgap prevents the hose from a possible connection to the waste water. I have also seen these fittings on the drains for commercial sinks where a hose can be dropped into the water.

Well, heat pumps use a drain pan to catch condensate in the event that the normal discharge route gets clogged up. But as for the plumbing, most codes require an air trap and an indirect connection to the waste line. I’ve seen many instances of the condensate line ending in an elbow joint that sits on the edge of a larger pipe coming out of the floor (as per your description) but I don’t think this arrangement has a special name. I’ve also seen some cases where the condensate line runs to a drain in the floor similar to a shower drain. Something like the last picture on this page.


This is only one part of the reason for having an air gap, in fact what your talking about is more of an anti-siphon measure. You’ll also usually see these inrestaurants. Under the sink, the water will go down the drain about 3 or 4 inches, then there’ll be a 1 or 2 inch gap where the water will fall into a larger diameter pipe (or a large dia to small dia coupler sort of like a funnel) and then it will go through the trap and into the main drain. This is so that waste water can’t back up into the sink. If you are thawing something in the sink under running water, or have any food or even clean utensils that are air drying in the sink and waste water backs up into it, you may not even notice it and wind up contaminating alot of food. This way if it backs up it just spills onto the floor and can’t get to the food.