I am looking to purchase a house where the location of the washing machine is such that the drain needs to pump water to a location higher than where the washing machine would sit.

The existing drain line has a one-way flow valve installed about 2-3 feet beyond the point where the washing machine would connect to the drain. That 2-3 feet is a vertical pipe so it would seem that the water in that pipe is at risk of draining back into the washer.

We have had a general inspector and a plumber look at the setup and they both claimed it was odd and I should install a separate pump system to make sure no water drains back into the washing machine.

I've never actually owned a washing machine before, do most washers have a pump in them already? Are there special models I should look at? Or do I need another system that can prevent the back-draining?

Realized I do have a picture:

enter image description here

  • This is definitely not a code compliant setup. It might work well enough to wash clothes, but it could potentially cause loads of problems as well. These problems can include, but are not limited to: Sewage baking up into the washer, dirty stagnant discharge water sitting in the washer, premature washer pump failure, gurgling/bubbling of nearby fixtures, sewage and/or gray water being forced up other fixtures, etc.
    – Tester101
    Commented Aug 30, 2017 at 14:08
  • Drain waste vent systems are designed to operate at atmospheric pressure, and to drain due to gravity. Pumping water directly into the system is not ideal, as it can cause sewage to be forced out places you don't want it.
    – Tester101
    Commented Aug 30, 2017 at 14:15
  • @Tester101 If you are willing to discuss a bit more, let us continue this discussion in chat at your convenience
    – FGreg
    Commented Aug 30, 2017 at 16:38

2 Answers 2


Washers have their own pumps. They are designed to pump water to heights "above them" but not generally "designed" to pump a longer run than the approximately 6' drain line they come with.

With that said, they will certainly pump beyond this amount, but based on how you run it, there is definitely a chance that the water that remains in the drain line can feed back in to the washer. This is not an issue if you are using the line the washer comes with. If you extend it, it can be a problem.

Also, with this said, your concern talks about the existing drain. I'm not too sure why there is a one way check valve either, (it is "strange") but it is not there for NO REASON. Either the current owner, or some previous owner had a bad experience with a sewer backing up, and if the sewer drain for this washer is at the "lowest" open point in this home, then the check valve would prevent that backup from visiting the floor via the drain pipe. More concerning is that THIS HOME may have had this issue. I would expect the homeowner knows this but it is possible they do not if the valve was already there. It is also possible the sewer issue causing it may have been fixed outside of the home. (if this is indeed why it is there at all).

Next.... You asked about the washer pump, but please realize that with the check valve there, the sewer wont by-itself back up into the washer. more importantly, since you DO NOT seal the washer drain pipe to the sewer drain pipe, if the sewer were to backup, your washer water and or sewer water would primarily end up all over the floor

If you have a wash basin, you would want to drain the washer into that, and then have a separate pump to drain the wash basin. That might be an ideal solution.

  • Thank you for your comments. The seller claims that was how the system was originally installed (approx. 1980). They had a plumber come in and look and of course they claim no external pump is needed. So my guess is our guy is quoting the cost of the "ideal" solution and there's is quoting the practical solution. I'm trying to gather more info to decide :) thanks again!
    – FGreg
    Commented Aug 30, 2017 at 3:28
  • I'm sticking with the idea "that it was put there for a reason". If the owner is original, I smell more fish, or sewage. Might be enough reason to request a sewer inspection. Is it septic or public? Is the property in a valley or base of a hill? You could probably even phone the local town municipality to inquire on overall sewer health in that area. Inspectors come in all shapes, sizes, and quality. Does the system TRULY look original from top to bottom? Or does it look like it has been serviced many times, with changes or mods elsewhere in the system?
    – noybman
    Commented Aug 30, 2017 at 3:35
  • One more note! Think of a fish tank or a siphoning setup: as long as the water table your washer is pumping into will clear the trap via weight and gravity, you are OK, but you still would want a wash basin as a reservoir in case the drain in itself gets clogged.
    – noybman
    Commented Aug 30, 2017 at 3:43
  • Realized I had a picture I could add. The sewer is public and the property is 5-10 miles south of some mountains, so past foothills but still general grade away from the mountains. I would think the check valve would prevent sewer backup, it's the section of pipe between the check valve and the washing machine that holds water that I'm concerned with.
    – FGreg
    Commented Aug 30, 2017 at 4:15
  • Where will your dryer vent go? Ideally I'd still (personally) put in a utility tub with a pump. But seeing that picture, its very likely the plumber that installed it did so to avoid siphoning sewer water with a wash machine hooked DIRECTLY to the line, with no air gap. It's not something I would do for the same reasons it sounds like you wouldn't. But it appears the homeowner would know if it worked. Did they use it?
    – noybman
    Commented Aug 30, 2017 at 11:52

If this helps, I have a similar setup in my basement, to avoid using a sump pump. I do not have a check valve, but that's a great idea. I've been running the same washing machine like this for 15 years now.

It may not make it technically correct, but it does work fine. Never had any issues.

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