View Full Version : Design, connecting shower and washing machine drain to the same sewer pipe.

10-17-2010, 06:16 PM


Design brainstorming, connecting shower and washing machine drain to the same sewer pipe.

My wife asked me to move the washing machine and dryer in the basement. The house is built in 2005 and the basement is not finished.
I attached 2 sketches of what it looks like. Things in black exist already, things in green I plan to install, to make my wife happy :o.
The builder left an opening in the cement slab where I can see the end of the exiting horizontal drain pipe. It’s 2 inch in dia. and has a plastic cap on it. I cannot be sure where the other end of this plastic pipe goes but judging by the angle it must come from the same vertical drain as the future sink.
As I showed in the first sketch, I’m planning on adding a p-trap to the shower and one to the washing machine (inside the wall, at the back of the shower cabin), then I would go horizontally north and merge the 2 drain pipes somewhere before connecting to the existing drain.
I actually prefer the second sketch. This would ease the installation because I would not need to break too much from the cement slab to pass the pipes. In the second design I connect the washing machine drain pipe to that of the shower using a T so that to avoid using two parallel pipes.

All pipes are 2 inch dia.

My question:
Would both these designs work properly? What can I do to make sure the water from the washing machine does not go up in the shower?


10-17-2010, 07:06 PM
You've got a lot more learning to do before you take this on.

Have you ever seen a fitting like this before?

What is the plan with the toilet?

All of your drains require vents...

10-17-2010, 08:16 PM
dlarrivee, I'm sorry for not mentioning this, but the builder said he already installed the vents and drain for sink and the toilet. He also left the opening for draining the shower. I only have to connect it.

10-18-2010, 06:20 AM
I see the shower drain becoming a geyser...

10-18-2010, 09:26 AM
I see the shower drain becoming a geyser...

No, no, the shower is not installed. All the green items in the sketch are future. I just need to make sure the design is correct.

Thank you for your help.

10-18-2010, 10:59 AM
You CAN"T run the drain line right under the shower opening and still install a "P" trap properly. The horizontal 2" line will create enough resistance, that the washing machine water will probably back up into the shower, unless the horizontal line is at least 18"-24" below the floor. Plumbing codes, and good practices, do not allow the washing machine to connect ahead of a floor drain or shower anyway. It is called "a major fixture over a minor one". Depending on the toilet opening's dimension from the two sides you may be in the market for an Eljer "Triangle" toilet to fit into the corner.

10-18-2010, 07:56 PM
hj, If I understand correctly your message, I have to run side by side the 2 pipes and merge them just before connecting to the existing drain (like in this image). This whay there should be no back up in the shower. It's going to be a lot harder to dig under the slab and pass 2 pipes instead of 1 but I have no choice. Thanks for the advice.

10-18-2010, 08:54 PM
You're going to need to run a 2" vent on the washer to wet vent the shower. The vent needs to go up through the roof of the house.