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Question DetailsAsked on 5/23/2017

sub pump drain for out side

I have a 2" schedule 40 sticking outside the from the sub pump, I want to dig a 8 or 10in. deep trench under ground, and use a Y and attach one end to the guter from the roof and the other from the sub pump and use a 4" pipe going through the sidewalk a curve. Should I use schedule 40 of sewer thing wall pipe ?????

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1 Answer


If you dump a sump pump outlet into an underground drain, leave an airgap and surface drainage swale for the discharge to do through in case the underground line gets blocked with roots, leaves, silt, roof debris, ice, etc - because you do NOT want your sump pump discharge line backing up and preventing discharge of the water.

Generally, not a good idea to run both in one drain line.

Since you say a drain line 8-10" deep presumably you have zero frost penetration depth in your area.

Normally one would use 4" dual-plastic drain pipe for this - looks like this, black poly inside and white PVC outside -


though regular Sch 40 PVC or HDPE drainfield pipe would also work at a somewhat higher cost. There are fittings available to go from 2 to 4" pipe (though I recommend using 4" pipe inlet with air gap) and for downspout to drain pipe (though again I recommend an air gap instead.

Another way to handle possible blockage backup is to use the adapter for the downspout (which is pretty tight fitting) but put an open-leg upward facing wye above it for overflow if needed so the downspout does not risk backing up to the gutters.

You should have a controlled drainage swale for any overflow to prevent wster buyilding up at the foundation area if the underground blocks off, and flush it out by running a hose with jet nozzle through it every year to three depending on how much roof debris you get coming down the downspout.

If this will be driven over by more than a rider mower, use solid steel/iron drain pipe at that depth - black iron better than regular steel.

Answered 3 years ago by LCD

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