URGENT! Washing machine drainage backing into kitchen sink!

[Christopher E. Shorter]

I’ve installed a stacking washing machine in the kitchen of a flat with an ABS drain running from the washing machine approx. 5ft over to the main kitchen sink drain. The washing machine drain joins the main drain just above floor level (below the sink p-traps). The washing machine manual states that water pressure from the machine is approx. 17 gallons/minute. Once the drain cycle begins, the water starts coming up the drains of the double sinks to a level of about 6″ where it sits for 30 seconds before draining in a normal fashion.

As the house is old (1920s) it is possible that the cast iron drain pipe has rust build up which is limiting the flow but given it’s location under the floor, any replacement would entail MAJOR renovations. The kitchen sinks drain very well on their own.

The washing machine must be located in the kitchen of this second story flat so their is no relocation option. Is there any way to decrease the water pressure from the washing machine so that the sink back-up is eliminated?

The manual mentions something about a “Siphon break Kit” (which my hardware store was clueless about). Would this solve the problem? Any help I can get will be greatly appreciated as my tenants are moving in on Monday!! Thanks!

[Retired plbg1Participant]

Your sink drain is partly stopped and it wont take it. Have a Plumber come and clean out drain and if it dont work find a bigger pipe. A 2″ pipe is smallest drain you can run a washer in and if it is stopped well you found out, besides if you did not put a trap on the drain you are getting sewer gas in your house. Better call a Plumber.

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Art retired plbg

[nicktheplumberParticipant]

Your problem is, technically, not in your sink drain, since that seems to work ok by itself. Your problem is that the common (“main”) drain, shared by your sink and the washing machine, is unable to handle the flow discharged by the washing machine. As RP says, a 2″ drain is the code minimum for a washing machine. Some kitchen sinks are plumbed with the minimum 1 1/2″ drains, or even worse, with 1 1/4″ drains…

When you have a kitchen sink AND a washing machine draining into a common waste line, that line should be big enough for BOTH fixtures to drain simultaneously. This means that the common drain should be at least 3″. Furthermore, the venting must be adequate. If you have adequate plumbing, your problem could be a clog in the main just downstream from the sink. Try snaking the pipe through the sink drain.

BTW, I appreciate that you are stuck with you layout, but ideally the washing machine should enter the drain downstream from the sink.

NtP

[paddysParticipant]

Thanks for the guidance guys. Given the concensus that the drain servicing the sinks most likely doesn’t have the capacity to take the washer flow without backing up, I’ve put in an ABS drain straight down through the inside wall of the 1st floor pantry to the basement where I can hook up with the main drain.

Looks like all will be ready for the tenant’s move-in tomorrow! Thanks again for the much appreciated guidance. This is a great site!

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