Potable Water Line to Trap


The attached picture is of a 3/8 inch water line that is connected to the cold water line under the sink in a bathroom. The bathroom is a full handicap bathroom with a shower designed to roll your wheelchair in, and a 2nd drain in the middle of the tiled floor for the occupant to drip into after the shower. This is the trap for the floor drain.

I wrote this up as a health safety hit because I don’t think you can connect potable directly to the drain like this. I got a call from the person who remodeled the bathroom saying that is was required for code for a drain that doesn’t have a fixture on it to allow you to put water in the trap. I told her I needed to do some homework.

Can you guys help me out? I am not finding it in the residential code. Mayby the plumbing code? I don’t have that one. This is a single family home. At a minimum I would think it would need some type of vacuum breaker or air gap type connection. I didn’t see it, but I am told it has a checkvalve.

Appreciate your input.


That connection should go to a trap primer and would be required to maintain the water level in the trap so no sewer gas will escape. http://www.plumbersurplus.com/ProductList.aspx?Cat=776

Regards Bill

There are multiple references but a direct connection between the potable water supply and the the waste system is not proper.

2003 IRC:

What you have pictured is an attempt at a trap-primer, but as Manny has pointed out, it has been improperly installed.

There must be an air-break (air gap) or a mechanical back-flow device.

How do we know its been improperly installed there is no picture of the connection under the sink. There may be a trap primer under the sink.
Regards Bill


Good point and only John can tell us for sure:

Based simply on the picture, it’s improper, regardless of anything upstream of the copper line.

You cannot attatch to a drain line in this manner. Approved fittings are required.

It is attached below the weir of the trap.

If that copper line has an air-break or a check-valve, it then becomes a drain line (after the point of the break or valve), which would require a downhill slope.

Great point
Thanks Bill

Unfortunately I didn’t take a picture of the connection below the bathroom sink where it is tied to the potable line. It is a regular compression fitting shut off valve connected to a Tee in the potable line before the sink shut off valve. The subcontractor that installed the line says that there is a check valve. If I check that valve, and it is a trap primer or vacuum breaker valve, it might be ok. But, as Jeff pointed out, it would still need to be above the weir of the trap. Anybody got one of those real good diagrams that they could share?

No. It’s still not okay, even if it’s above the weir. It must have approved fittings, and it must slope down to the drain.