sink drain causes shower to back up

12 years ago

I live in a 1921 apartment building. Each floor has two mirror-image apartments, and each apartment has two bathrooms, with the smaller bathrooms being back-to-back. So they share water supply and master drain lines.

The shower in the little bathroom started draining slowly enough that it would back up. When we put Liquid Plumber down, it helped a little. Then I plunged it, and that helped even more. Another dose of Liquid Plummer a few days later, and it seemed to be able to keep up with the shower flow.

HOWEVER, my son pointed out that when the water runs for a long time in the sink, the shower drain backs up. (It apparently was a faster reaction earlier; but the reaction is still there.)

What could be causing that? And do we need to do something about it so it doesn't get worse?

I don't think there's a U-bend directly under the shower; I don't think the floor is thick enough. I don't know where the U-bend would be. The drains all join into the master drain pipe (I'm pretty certain).

Sort by:Oldest

Comments (5)

don_1_2006
12 years ago
This is one common symptom of a blocked drain. The shower drain is lower than the sink so the backup occurs there. Have your drain cleaned.
talley_sue_nyc
Original Author
12 years ago
Is it likely that the blockage is lower even than our shower, since we're in an apartment building (2nd floor)?

It takes a while for the backup to hit us, so it's probably coming from below--yes?
Related Professionals
Harmony Plumbers · Wolf Trap Handyman · Bellevue Kitchen & Bathroom Remodelers · Blasdell Kitchen & Bathroom Remodelers · Camarillo Kitchen & Bathroom Remodelers · Channahon Kitchen & Bathroom Remodelers · New Port Richey East Kitchen & Bathroom Remodelers · Olney Kitchen & Bathroom Remodelers · Port Angeles Kitchen & Bathroom Remodelers · Rancho Palos Verdes Kitchen & Bathroom Remodelers · Spokane Kitchen & Bathroom Remodelers · Sweetwater Kitchen & Bathroom Remodelers · Phillipsburg Kitchen & Bathroom Remodelers · Westminster Kitchen & Bathroom Remodelers · Forest Hills Kitchen & Bathroom Remodelers
talley_sue_nyc
Original Author
12 years ago
I've been thinking about this--even if the clog is in the walls, it has to be below us and above the first floor--otherwise, it'd back up in the apartment below us, and never in ours.

Right?
don_1_2006
12 years ago
If you are having a problem but the people below you aren't it must be in the wall between the 2 apartments. If the stoppage was after their apartment they would be getting all your waste.
aidan_m
12 years ago
The clog is most likely in the 2" horizontal line serving the sink and shower. There is a wye in the line, splitting off the sink and shower. The clog is after the 2" wye, but before the 2" line tees into the main 4" vent stack. The best place to attempt access (if there is no cleanout) is the shower drain itself.

Showers usually have a 2" drain right in the floor. A flexible snake 1/4" diameter can pass through this line. Getting past the p-trap is the hardest part, but it is possible. Once past the p-trap, it will be easy to pass the snake all the way through to the main 4" vent stack. I'll bet you pull a tennis ball sized clump of hair out of the drain.

The plunging and liguid plummer dislodged the clog from the shower p-trap and sent it a down the trap arm, just past the sanitary tee. After the sanitary tee, plunging is no longer effective, because the drain is vented past that point. Plunging it just pushes air up the vent stack! You must snake out the lines now.