Hot Topics: Plumbing a Laundry Room

A laundry room in need of a new sink and drain.

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The plumbing in a laundry room is often exposed, making it simple to work with, but laundry rooms are often afterthoughts in basements and garages, making the plumbing more complex. As one member sets out to take on the tangle of pipes, the forum helps straighten them out.

Original Post: Correct way to pipe this for washing machine/laundry sink

jasesun23 Member

Hello guys. Could use some advice on the best/right way to set this up. Pics included. My old sink/metal cabinet setup was completely rusted so I removed it. Upon inspection of the pipe, it was rusted going down in the drainpipe so I removed all of it. It just lifted out of the drain on the floor. So now I'm left with setting it up and running some pipe.

Background — this drain does not seem to go to the septic tank as all the other waste pipes do. You can see the septic line 4 feet above. I believe this goes to a dry-well under the driveway. It is a 2-inch pipe that a 2-inch donut fits into snugly. In the old setup there was the black flexible drain pipe from the washing machine that went directly into the piping, not into the sink. Also, there was a heavy black hose going up 7 feet and ending in the beams below the ceiling. I'm assuming this was some form of a vent (however it was not venting outside).

Ideally, I'd like to drain right into the pipe as opposed to the sink if that’s allowed.

I plan on putting a countertop from the shelves on the right all the way to the washing machine on the left, then cut out a section to put a drop-in plastic laundry sink. I'd rather not cut another hole into it to run the washing machine's drain pipe into the sink. But I will do whatever is best/correct. It’s the laundry room and I don't care too much about how it looks.

Highlights from the Thread:

lawrosa Group Moderator

Drain the washer to the sink. I would still use that dry-well unless there are issues with it. You need to vent the sink with a studor vent.

If you’re wanting to tap into the septic line then a pumped system is the best approach. The pump system gets vented.

jasesun23 Member

Thanks for the quick reply lawrosa. I am planning to use the existing drain into the dry-well. No plans on tapping into the septic tank.

So knowing I'm adding a sink with a p trap into the existing 2 inch drain going to the drywell I should:

Drain the laundry into the sink like the yellow line in the picture below? No way to tap into the plumbing I’m going to have below the sink, like the black line in picture? Kind of like a dishwasher drain branches into the kitchen sink plumbing. Why couldn't I go directly into the plumbing below? Is there something against code?

I will look at studor vents as I am unfamiliar with these. I don't believe there are any vents on the pipe going to the drywell. The only thing I think that goes to the drywell is the basement sink and washing machine. There are a bunch of vents with the septic tank plumbing.

Plumbing a Laundry Room2

lawrosa Group Moderator

You do not want to tap into the line with the washer. It may flood the pipe and not drain. The sink acts as a buffer. Plus it gives the required air gap. It’s just all around better. If the line backed up the sink would hold the water and not flood the basement.

You want to raise the studor vent 3 feet above the flood plain of the sink. You can do this because you’re all open down there.

jasesun23 Member

Thank you, lawrosa. I'll empty the washing machine drain hose into the sink. Seems like the easiest and best way.

I'm curious though if you have a second to explain. If I choose to attach the drain hose somewhere above the p trap of the sinks drainage system, how would this be different than how my dishwasher is hooked up to my kitchen sink. And if the piping I used is 2-inch, should it not drain fine.

Thanks again and enjoy your weekend.

Furd Member

With most washing machines you need to have the drain hose rise to the top of the cabinet before it drops down. The reason is that otherwise, the tub will never fill but just drain as fast as the water enters. You can't just bring the hose up and then down again as it is likely to siphon. That is one reason why the drain hoses have the curve and are as short as they are.

lawrosa Group Moderator

Code requires a standpipe for the washer of at least 18" if you do not dump into a laundry sink.

jasesun23 Member

Got it. Last question--can you just confirm the piping is okay for what I need to do. There will be two 90-degree elbows at the bottom so I can get the pipe against the back wall. If I don't do this and run the 2-inch pipe straight up with the studor vent on top it will be a foot out from the wall.

Furd Member

I would suggest two 45-degree bends rather than the two 90-degree bends if it won't cause any other problems. Much less chance of clogging from lint and such. Also much easier to snake if that ever arises.

See all the diagrams, the completed install and find more advice in the original post.