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Question DetailsAsked on 9/26/2017

can i connect smooth pvc pipe to existing 4" yard drainage pipe ?

I have 4" non-perforated drainage pipe coming from house out into mid-yard (carries water from basement sump pump)
and want to extend from mid-yard 15-ft to shallow ditch (currently too much water for yard to handle during wet seasons). Other alternative is connecting 4" perforated drainage pipe (using lawn fabric and gravel) but would require much larger ditch; would also use use fabric and gravel with PVC and drill holes in PVC for leeching, or is there smaller than 4" perforated drainage pipe available that can be attached to the existing 4" ??

Thanks for any suggestions / recommendations.

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1 Answer


Sure. Unless you want that new 15' run to act as an infltration gallery (and assuming the slope/topography is such it cannot get back to your foundation and that the soil is pervious and permeable enough to act as a drain field) then use solid pipe. If you want an infiltration zone there (and in that case be sure to put an impervious clayey soil plug in the ditch at the uphill end if there is any chance it could back up to the house if the pipe freezes or plugs up) then yes you would need a larger trench - typically about 10-12" minimum - for the surrounding filter pack gravel.

If you go with the perfroated pipe there are three potential ways to handle it depending on the result you want - one row of holes down and other to the side, so anytime the water flows it exits the pipe into the gravel - though the bottom holes can plug up quickly with silt and debris if anything other than sump pump feeds into this, holes centered and pointed down (so angles d out at about 30 degrees) to drain out into the surrounding soil whenever the flow is substantial - but a low flow will flow in the bottom of the pipe between the two rows of holes without going into the ground. Third way is holes up, so it exfiltrates only if the drain line is blocked or running near full - this is a common backup, with a gravel filled pack around the pipe (maybeonly a couple of inches all around) to act as a reverse french drain if the pipe gets blocked - letting the water flow through the gravel alongside the pipe to the exit.

Otherwise, solid pipe - which can be the same type of pipe as the existing, or a plastic pipe as you say.

Connecting together - first, you do NOT want to decrease pipe size downstream - that is acsking for trouble, plus easier to clean out 4" than smaller pipe. Connections of same-size pipe of course can be by blued bell joints or glued couplings with plastic, or threaded connections with almost any kind. Cast iron and mis-matched pipes you can join with a special adapter coupling (typically about $40-60 for specialty 4" couplings) - or since this is a non-critical unpressurized pipe, just a no-hub coupling whould work just fine. Look like this - and available for bare pipe and for coupling ends for vrious types and sizes of pipe - both same-sized and same general pipe size pbut somewht different outside diameters. Look like this - I have shown typical metal pipe coupling, pretty much any type of pipe coupling for same-size pipe, and different-size pipe versions (a similar verion is available to connect bare pipe to a coupling end which is somewhat larger):

The key is you want to avoid a smaller diameter downstream pipe as that will catch any debris, though if only a sump pump discharge going through it that is not a concern - but 4" pipe is not expensive (especially the plastic drain field type) so I would stay with 4".

Note you did not say WHERE you are - if in an area with freezing ground winter conditions then your drain pipe needs to be deeper than frost depth or it can freeze up if significantly below freezing (warmish disharge may prevent freezing if ground is not much below freezing for long). Best practice is to assume the drain pipe will freeze up and put the sump pump discharge into a vertical section, loosely fitting and with an airgap between them so if the drain pipe freezes solid the water will overflow at the inlet onto the ground. Of course, the ground there should slope away from the house to drain so it doesnot come back through or under the foundation, or right back to the sump pump. Generally in area with frost depth of more than a foot or so, is commonly better to go with a swale or ditch with impervious bottom to drain the water away, with enough dimension to accomodate a signifiicant amount of icing up.

Answered 3 years ago by LCD

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