Shower backup when doing laundry

[iknowaguy]

Hello all,
I have a small issue I am looking to fix while I am remodeling my basement bathroom. See attched very crude diagram.
Basically the washer drains into the utility sink wich has a 1.5" ptrapinto a 1.5" drain with an AAV. This same line goes into the bathroom next to the laundry room which picks up a sink which also has an AAV. This line ultimately goes below the basement floor and ties into the main sanitary line. Also in the bathroom is a stand up shower which ties directly into the main sanitary line under the slab.

When ever the washer drains, water sometimes comes up through the shower pan, then drains back down. It ultimately drains, the water is sucked out of the p trap. I have the walls opened up and would like to fix the issue.

 

[Reach4]

Your clog is downstream of where the washer drainage joins the shower drainage.

Get your septic tank emptied if you have one. Otherwise, get the line labeled main sanitary line/exit house cleaned to the city sewer. You could have roots in the line under the lawn.

Be glad you noticed this now.

 

[Sponsor]

 

[WorthFlorida]

If you are opening the floor at all installing a sewer backflow preventer would be an advantage. Any backup from the city sewer system will unload into your basement from the shower drain.

 

[cyphergt]

How old is your house? I know that in my home the issue was at the sewage cleanout plug we have an old P Trap before going out to the municipal sewage system and it had a fatberg.

 

[Terry]

The lines need snaking to clear them, and the shower needs it's own venting.