Minor low spot in rainwater drainage wye - acceptable?

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SonOfGloin

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Hi all,

Long time lurker here, finally stepping out of the shadows for some advice (which I've received plenty of over the years reading these fantastic forums!). This is actually in regards to underground rainwater drainage, but since I'm using ASTM d2729 sewer and drain pipe this is a fairly generic plumbing question.

I'm installing two gutter drain tiles that connect to a single 4" pipe that I (painstakingly) tunneled under a masonry walkway. This is depicted in the attached photo; the walkway is to the left, one drain tile is at the top, and the other will eventually be installed in the upper right.

IMG_5202.jpg


I was able to just barely make minimal grade with the S&D pipe under the walkway. I opted to solvent weld a wye here, rotated 45 degrees to connect to the first drain tile. However, despite triple checking everything with dry fits and a level, much to my disappointment the wye tilted slightly after the solvent weld and is very slightly back graded (that is, graded toward the right in the photo). Water from the upper left drain tile unsurprisingly smashes down to the center of the wye and drains nicely as the water level rises, but a small amount pools down the right side . Here's a photo where I dry fit a 45 degree street elbow, just to see how much water will pool there:

IMG_5199.jpg


Naturally, when the elbow is eventually solvent welded, it'll be more flush with the hub, but this give you a good sense of how much standing water will always be there.

My question for the mind hive here is whether this minor pooling is acceptable in this application. Potential concerns are whether this perennial small pool of water will cause debris accumulation, and whether mosquitoes might breed down there (I'm not sure how far away from the surface they can go to access this breeding ground). On the other hand, the right side drain line is sloped significantly enough that downpours will likely wash over the low spot in the wye with regularity, and I could always seal up the downspout adapter to prevent any mosquitos from even thinking about it.

Concerns with cutting it out and starting over: I don't have that much "meat" in the pipe that goes under the walkway, and since solvent welding is a quick and stressful 30 seconds for me, there's a chance that the new wye would still have a dip spot anyway. I'm sure there's a more efficient or mechanically correct way of designing this in contrast to what I've done here, but as you can see in the first photo I have to be really careful with the gas line right there (which is why I opted for the wye where it is and not at the base of the upper left drain tile).

What do you think? Am I being too anal? Any advice from the pros and fierce DIYers is appreciated.
 

breplum

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Aside from not knowing the mosquito breeding access question, I think you may be ok, as long as the flushing action from the right won't have any detritis of consequence.
I've seen domestic building drains that clogged from slight back tilt while still receiving stack flushes from one story above !
 

Reach4

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Looks nice. A leaf blower can be used to help clear that line of leaf material if you ever need it, but you would want a way to block other paths.

I have heard that 1 inch per 10 ft drop is good for gutter water outside.
 

John Gayewski

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I think i would connect the piece of pipe to your wye and let the glue dry and then put some rock under the pipe. You might find that picking up on the continued pipe will give that fitting some grade.
 
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Jeff H Young

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well its not optimal but is it going to plug up every time it rains ? no . its an improper installation not desireable but it might not ever cause a problem. take a chance or dont the call is yours . I dont know whats going down it in a perfect world crystal clear rain water wouldnt hurt a thing, in a not perfect world it might not in years cause trouble , but no guarantees it will last a season if tons of leaves come down
 

Reach4

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Jeff H Young

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trick to force pipe up some is a good one I thought it obvious but not really I guess we that been doing this would likely try it but not everyone would think of it
 

SonOfGloin

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Thanks for all of the insightful replies.

Regarding the mosquitoes, I spoke with a local insect expert and, much to my surprise, it turns out that the asian tiger mosquito (e.g. the bane of my existence) can find its way that far into the piping and use the standing water to breed. However, blocking access with some screening can prevent this. I think I will go with some copper mesh and stuff it in the gaps between the downspout and the drain tile adapter, which will eventually look like this when the job is done:

IMG_5204.jpg


That's an SDR35 adapter and there's plenty of room to stuff the mesh in there. Looks like that problem is easy to solve.

Putting the rock under the pipe is an interesting idea, and something I've entertained. However, the wye is very difficult to lift with muscle power, so I'm not sure how much it'll budge. There's very little meat on the lower left piping (the one that goes under the walkway) to move with the wye. But I suppose it only has to move slightly.

Regarding debris: the downspouts that feed these pipes will have leaf protectors installed at the gutters' drain outlets, so no large leaves will ever make their way down to the wye. Smaller debris is still fair game.

Perhaps it's worth installing a cleanout immediately upstream of the wye, then. So something like this:

IMG_5202 copy 2.jpg
 

Aaloo

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Consider adding a downspout leaf filter. https://www.homedepot.com/p/Amerimax-Home-Products-Flex-Grate-White-Vinyl-Downspout-Filter-4490/205076357
are examples.
So far so good a nice suggestion
 
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