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I’m at a crossroads and could use some input. I’ve been laying pipe to carry greywater from our two bathrooms to trees and mulch basins in our front yard, which lies slightly down slope from the fixture drains of the front bathroom in the crawl space. My plan all along has been to rely only on the slope to deliver the water. What I’m finding, however, is that I have extremely little margin of error because the slope is so slight, at least if I am to follow the code of 1/4 in per foot. More concerning still is that, in order to use every needed millimeter of vertical descent through the crawl space, I would have to drill holes in the floor joists across the width of the house, some of them on the outer thirds of the lengths of the 2×6 joists and in the middle third of the span of the joists (both against code). Now, I have talked to an engineer, who thinks that with stud shoes, I can drill the holes without compromising the joists, hopefully to the satisfaction of a home inspector, should we ever have to sell our home (not something we anticipate). There would be relatively inexpensive ways of otherwise reinforcing the joists if necessary.

But I’m starting to wonder if I need to let go of my commitment to power the whole system with gravity. With a lot less up-front hassle, I could install a drain basin and sump pump or the like on the edge of the crawl space (or just outside), pumping the front bathroom greywater water up to the greywater drain pipe at the necessary height alongside the house. That pipe would join with the pipe coming from the back bathroom, which, because of its location, has a steady slope from the back of the house to the front yard. So I’m starting to toy with the sump pump alternative, but I’m torn because this adds another technical dimension to the system, the need for electric power (which is not too difficult to deliver), and potential pump malfunctions or loss of power with the resulting flooding (unless a good back-up system is in place).

What do you think is the best way forward? Enough experience with pumps to say whether they’re reliable enough? Hope my description of the dilemma is clear enough. Thanks.

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Sorry it’s taken so long for you to get a response to your question!

Your description of the situation sounds clear, and there are pros and cons of either option, like you mention. Pumps can be reliable, so if you need to pump the water it should work fine. A sump pump won’t be the most reliable option though, get an effluent pump rated for 3/4″ solids.

I would also consider having two separate systems. It sounds like you can install one gravity flow branched drain system from one of your bathrooms. You’ll have a much easier time distributing the water from that system if you don’t include more water into it. The bathroom that isn’t easy to install via gravity, you could use a pump to direct the water all the way into the landscape and use a laundry-to-landscape style irrigation system- this will be much easier and less time consuming to construct than a gravity flow system. You could also consider a saniflo pump (made to pump shower water from a basement up to the sewer line). That system may be strong enough for your application- you can check the specs.

Hope this helps, and write back if you have more questions! (I’ll answer in a more timely manner)

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