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Question DetailsAsked on 7/27/2017

Why does the groundwater basement sump pump run when upstairs toilet on septic system is flushed?

Have done the following recently:
1) Ejector pump float replaced
2) Septic tank pumped
3) Lift station pump replaced
4) Broken main line pipe replaced

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2 Answers


OK - Angies List system is taking paragraph breaks out AGAIN - everyplace a nnnn appears should be a paragraph break.



Sounds like possibly the toilet DWV (drain, waste, vent) piping is leaking, allowing leakage (or septic tank overflow) to come back into the basement as "groundwater", making the pump run. Generally, unless a pipe leak was going pretty much directly into the basement, there would be a significant delay between the flushing and the sump starting to fill, as it takes time for the water to percolate to the basement underslab drains/sump.

nnnnnn Also, if this was the case, one would expect every water point-of-use would cause the same effect - and especially so with washing machine and emptying tubs. nnnnnn Otherwise, sounds like someone plumbed the sump pump into the DWV piping and poor piping arrangement or a backup/partial blockage in the piping to the septic tank is causing backflow to the sump pump - in which case the effect would be almost immediate. Sump would also be getting very nasty and sewage smelling very quick. nnnnnn If ONLY the one toilet using water is causing this, not any other toilet or sink or washer or such, then sounds like the sump pump was connected to the branch that the toilet feeds to, fairly high in the plumbing system, so other consumption points are not causing water to run to the sump pump. nnnnnn Sump pump should NOT feed into the DWV pipes, though some DIY'ers and some plumbers do that, and sometimes it is done by a homeowner because the discharge to the ground is freezing up in winter. Generally illegal if on public sewer, may or may not be legal on a septic system but puts unnecessary water into the leach field. Should drain to a natural drainage downhill from and as far as practical from the septic system to keep that groundwater drainage out of the leach field. nnnnnn Sounds like tracing the piping from the sump pump (and making sure no DWV pipe is feeding to it also) is the thing to do. nnnnnn Note I assumed you were right about this being a sump pump, not a sewage lift pump - the latter is enclosed, not a pump standing in an open to air (though possibly with floor cover over it) sump. nnnnnn Another thought because of all things you have had done (hopefully not in the course of trying to solve this problem) - if the sump pump is discharging into the DWV piping, this may be a new problem if the lift station you are talking about is indoors - so lifting basement sewage to upper level. if repalced, it might be pumping at a higher rate than before, so it is filling the lines up more and causing backflow through the sump pump connection, which it might not have done before. nnnnnn One other alternative- if in-house ejector pump (sewage grinder/lift pump) and the housing is leaking sewage from that might be leaking very rapidly to the sump under the slab. However, once again, would expect the sump pump operation from every consumptive use in the house of any significant amount, not just the upstairs toilet - so sounds more likely the upstairs toilet is on a separate branch which someone tied the sump pump into. nnnnnn If unable to figure this out yourself, sounds like a first-rate Plumbing contractor is what you need (your Search the List category to find well-rated and reviewed plumbers).

Answered 3 years ago by LCD


BTW - if the sump pump running is because of a direct piping connection to the DWV system, the water (sewage) would be coming out of the bottom of the pump into the sump before it starts pumping out again, whereas a source leaching through the ground to the underdrain system or sump pit would come into the pit directly - you should be able to see the gurgling and likely some air bubbling if coming out of the pump - also if you listed to the discharge pipe from the sump pump while someone flushes the toilet, you should be able to hear the water coming into the pump through the discharge pipe before it fills the sump enough to kick the sump pump on again.

Answered 3 years ago by LCD

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