# draining sink and washing machine into same pipe?



## FamMan (Aug 2, 2015)

http://callmetalman.com/wp-content/plumbing-question.pdf

I've attached a diagram to avoid any miscommunications here. I'm redoing a bathroom/laundry room and have a washing machine and sink that could easily be combined into one drain and vent, if it's okay.

Any other option would be a lot more work.

a) My biggest question is whether I can drain the washing machine and a sink into the same 2" drain/vent? If it's okay, then I assume the sink should drain above the washing machine, correct? 

b) what's the minimum length required from trap to pipe on the washing machine (see pic)?

c) whats the maximum length allowed from sink trap to pipe? (I can install a cheater vent, but at 1/4" drop per foot, it only buys me so much extra.)

d) last, unless I've overlooked a question, what is the required height of the washing machine trap and sink trap?

Thanks for your help. I've spent a lot of time staring at this to try and figure out a plan, but with these questions lingering, I'm at a stand still.


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## jmon (Nov 5, 2012)

your logic seems sound. You put a lot of thought into this project. The plumbers will be along shortly to discuss codes, etc. Ipc vs upc ect.

Just to clarify, there are no other fixtures draining into the vent line from above, correct?


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## FamMan (Aug 2, 2015)

Correct. just those two fixtures would drain into it, and I assume the sink should be on top.


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## FamMan (Aug 2, 2015)

Nobody? I thought for sure these would be ez answers for the right people.


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## TheEplumber (Jul 20, 2010)

FamMan said:


> Nobody? I thought for sure these would be ez answers for the right people.


The right people must not be here.:wink2: I don't know your code so I can't say for sure what you need to do. For instance-
Trap arm lengths vary. Vertical wet vent code varies. DFU's for washing machines and kitchen sinks vary per code. 
Also, suds relief code comes into play with fixtures such as washing machines.
But, to answer your questions based on UPC-
a) It would need to be 3" - the wet vent section is to be 1 pipe size larger than the drain served, which is 2" for both KS or WM
b)2 times the diameter of the trap arm
c)Washer trap must be 6" above the floor. No dimension specified for a sink trap height.
Again- these are UPC requirements. I briefly searched for your code but didn't really find an answer.


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## FamMan (Aug 2, 2015)

So, when I combine drains, it has to be one size larger. That makes it a 3" drain. Got it. 

Suds relief code?


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## Old Thomas (Nov 28, 2019)

Use a double sanitary tee so the drains are opposite each other. It is not a wet vent unless another fixture shares the pipe on a higher floor. 2” is ok.


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## FamMan (Aug 2, 2015)

Thanks. Big help there. That alleviates my main concern.

The only other concern is that a washing machine inlet (where the hose from the washer deposits water into the drain in the wall) is supposed to be above the top of the washer right? I'm, assuming that's to prevent backup from high pressure water not draining fast enough.

So I'm wondering whether having a sink connected, and the sink sitting at a lower point than the washer, could cause issues with water backing up into the sink, from the washer.

Probably not, right?

Any input?


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## huesmann (Aug 18, 2011)

If you had a blockage (even partial) in the pipe after the two drains connect, then having the sink at a lower elevation than the washer inlet could cause backup into the sink. If the top edge of the sink is lower than the washer outlet, then a backup could cause flooding. OTOH, backing up into the sink _is_ kinda like an expansion tank.


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## Ghostmaker (Mar 2, 2013)

Your under IPC code same as what I inspect. 



406.2 *Waste connection. *The waste from an automatic clothes washer shall discharge through an air break into a standpipe in accordance with Section 802.4 or into a laundry sink. The trap and fixture drain for an automatic clothes washer standpipe shall be not less than 2 inches (51 mm) in diameter. *The fixture drain for the standpipe serving an automatic clothes washer shall connect to a 3-inch (76 mm) or larger diameter fixture branch or stack.* Automatic clothes washers that discharge by gravity shall be permitted to drain to a waste receptor or an approved trench drain. 
*SECTION 407*

*Your upper sink can be 2 inch but where the washer sink drain's into the tee it must increase to 3 inch pipe size.*



*FIXTURE DRAIN. *The drain from the trap of a fixture to a junction with any other drain pipe.


*FIXTURE BRANCH. *A drain serving two or more fixtures that discharges to another drain or to a stack.


*The fixture drain for the standpipe serving an automatic clothes washer shall connect to a 3-inch (76 mm) or larger diameter fixture branch or stack.*

You cannot use this to wet vent the bathroom because a washer is not a bathroom group fixture.


*BATHROOM GROUP.*A group of fixtures consisting of a water closet, lavatory, bathtub or shower, including or excluding a bidet, an emergency floor drain or both. Such fixtures are located together on the same floor level.


912.1 *Horizontal wet vent permitted. *Any combination of fixtures within two *bathroom groups* located on the same floor level is permitted to be vented by a horizontal wet vent. The wet vent shall be considered the vent for the fixtures and shall extend from the connection of the dry vent along the direction of the flow in the drain pipe to the most downstream fixture drain connection to the horizontal branch drain. Each wet-vented fixture drain shall connect independently to the horizontal wet vent. Only the fixtures within the bathroom groups shall connect to the wet-vented horizontal branch drain. Any additional fixtures shall discharge downstream of the horizontal wet vent.


I would suggest you contact your local plumbing inspector and show him a complete drawing when you get your permit.


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