My house was built in the 1980s and when I was in my crawl space, having to replace the leaky check valve ( vertical orientation, right above the sump pit, then the drainage line turns horizontal leading outside ), I realized that my washer drains right into the sump pit and, of course, the sump pump then discharges it outside. ( This is perfectly legal and acceptable where I live )

I had to replace aforementioned sump pump about six months ago ( installed originally five years ago ) and I had read in another forum that, over time, lint in the washer drainage water, could be the culprit as to why sump pumps fail. Recommended solution: pantyhose over the end of the washer discharge hose. OK, that makes sense, so I will do that.

So my question is this: can I just route the washer discharge right into the sump discharge line, avoiding the sump pit completely, thus avoiding more wear and tear on the pump? It just seem redundant dumping it straight into the pit and then having the pump do more work. Presumably ( and I'm no expert here, obvs ), but I assume that would entail .....

  • Join the washer drainage line to the horizontal sump discharge line using a wye fitting
  • Join the sump pump drainage line after the sump pump's check valve
  • The washer drainage line, before joining the wye fitting, will need its own, preferably, spring type check valve in a horizontal orientation

I would positively love any input that any of you may have on this proposed ( and possibly completely erroneous ) schematic. I have learned so much lurking in this forum and hope this all makes sense. Many thanks in advance. JW

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    The washer lint might also clog up any other lines, but it does seem to bother other drain lines. Sump pumps seem to take other stuff so lint should not be a problem in normal houses. Five year replacement seems to be early, unless a very cheap pump(unless their quality as gone down shapely recent years).
    – crip659
    Commented Aug 2, 2023 at 22:57
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    What's the distance between the washer drainage line and the pump horizontal discharge line ? Are you sure it's still legal to do this?
    – JACK
    Commented Aug 2, 2023 at 23:06
  • I appreciate all the questions about legality but it's fine and that's not the point of my question. I am just wondering if the washer discharge line can be routed directly into the horizontal sump discharge line. Thanks Commented Aug 2, 2023 at 23:32

1 Answer 1


The simpler solution (if direct washer discharge is, as you say, legal in your area - which is unusual these days) would be to run a separate line for that directly from the washer to wherever it drains outdoors.

If you're dead set on using the sump drain line, you appear to have the basics down - though my experience with two sump pumps conjoined to one drain line (not by me) is that you might also want a vent (either a mechanical vent mounted as high as is convenient, or an open vent line up to the roof level) on the line at the Y location. The pumps can fill the line and the suction can flap and bang the check valves, causing "burpage" back into the sumps - a vent would prevent that.

You might (and here the "two pipe solution" is much easier) need to go to a larger pipe, or everything may appear to work fine, until the sump pump turns on while the washer is draining. I see a non-zero probability that the washer standpipe could overflow in that case.

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    OP does not seem to suggest two pumps, maybe joining two drain lines into one or adding a drain to a drain line.
    – crip659
    Commented Aug 2, 2023 at 23:31
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    @crip659 Nor was I. I was describing what I have seen happen with two sump pumps sharing one drain line, which is similar in concept to a sump pump and a washer sharing one drain line.
    – Ecnerwal
    Commented Aug 2, 2023 at 23:36
  • I see where a washer discharge pump can be considered as a de-facto sump pump. The washer overflow I can now see is a REAL concern. Accepted your answer @Ecnerwal . Commented Aug 2, 2023 at 23:39

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