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Replacing Kitchen Sink Drain

15 years ago

We had to rebuild the foundation and floor under our kitchen and disconnected the existing plumbing to do the work. Below is a picture of the stud wall with the disconnected plumbing. I inserted some fittings showing how the plumbing was previously connected.

We decided to move the kitchen sink location a little to the right and would like to move the Y connection for the kitchen sink from the vent pipe on the left to the 2" drain line from the washer on the second floor located on the right. See picture below showing the new unconnected arrangement.

I have the following questions:

Is it permitted to tie the Y connection from the kitchen sink directly into the 2" drain line from the washer on the second floor?

Is it better to use a 1-1/2" or 2" trap for the kitchen sink?

Thank you for taking the time to read my post and consider my questions.

Howard

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Comments (4)

homebound
15 years ago
Don't know (probably not), but why not simply "aim" the wye's hub out at an angle (instead of perpendicular) out the wall?
sequoia_2007
Original Author
15 years ago
The walls for two adjoining cabinets will land where the left drain pipe is located.
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lazypup
15 years ago
My first question is how in the name of all that's holy did they ever pass a code inspection on the original work?

The fitting that you have labeled as a "Long Radius Wye" is not a long radius fitting, it is a "Combo", which is simply a "Wye & 1/8th Bend combination" made up in one fitting. Code requires that when we connect a fixture arm to a horizontal line we must use a Wye & 1/8th bend or a combo but when connecting a fixture arm to a vertical line, such as your kitchen sink waste arm, we are required to use a "Sanitary Tee". A Wye & 1/8 bend or combo is expressly prohibited when connecting a waste arm to a vertical riser.

The reasoning for this rule is quite simple. A fixture arm has a dual purpose serving as both a drain line from the trap and a vent line to the trap. The general rule for a waste arm states that the bottom of the pipe at the "Trap Weir" may not be higher than the top of the pipe at the "Vent Opening".

If you will exam your combo from the side view you will note that the bottom of the pipe at the horizontal side input is higher than the opening into the vertical portion at the base of the Wye. If we then allow for the 1/4" per foot mandatory pitch on the fixture arm it is easy to see that the bottom of the pipe at the trap weir would be well above the top of the vent opening at the base of the side input on the Wye.

You may not connect the kitchen fixture arm to the 2" riser to the second floor. Code would permit two fixtures to be connected to a common vented stack providing the stack has No offsets and the upper fixture is not a watercloset(toilet) or receiving a powered discharge (the discharge from a laundry standpipe is a powered discharge.)
sequoia_2007
Original Author
15 years ago
Lazypup,

Thank you for the detailed explanation. Here is a picture of the original plumbing before replacement of the floor joist and subfloor.

Tonight I test fitted the connectors per your recommendation. It is basically the same arrangement as the original installation. The 1-1/2" horizontal pipe connected to the sanitary T is 16" above the subfloor.

Howard

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