I'm attempting to install a new sump pump in my basement after having a few minor flooding incidents and addressing as much of the external causes as possible (gutters, etc). The pump is only used for dewatering the foundation soil; nothing else drains into it.

I live in Rochester NY, which does allow connecting sump pumps to sanitary lines, which is probably the most reasonable option. I could entertain discharging to the outside, but there's not much avenue for that, given the geography and how little land there is around my house.

The sump is located 2 feet to the right in the below picture; discharge tube isn't connected yet. Bottom of the discharge has a standard check valve.

I was wondering what is the correct way to tie the sump discharge into to the sewer stack, pictured below:

Sewer stack picture

Question 1: What would be the easiest place to tie in?

I was thinking of tying into the 2-inch pipe on the left of the picture using a 45 degree wye pointing to the right, given that it has the most pipe to work with and is probably the cleanest to work with. I would run the discharge pipe up the wall on the right, angle it on top of the sill you see at the top of the picture, behind the existing iron-cast pipe, and down next to the 2-inch pipe on the left.

Question 2: Do I need any sort of p-trap? The discharge line has a check valve at the bottom of it, so there should always be a significant amount of water (10 feet) in the discharge riser to prevent sewer gas leaking back.

Question 3: Does the horizontal run of the pipe need to be sloped?

Question 4: Do I need an air admittance valve at the top of the discharge? The large pipe at the top-right of the photo has an air admittance valve about 10 feet off the floor, and I believe the pipe I'm tying into has an AAV, 2 floors up.

Question 5: How much height do I need off of the wye from the 2-inch before I go horizontal? I was planning on cutting into the pipe in the middle just for convenience.

  • 1
    @keshlam - "I live in Rochester NY, which does allow connecting sump pumps to sanitary lines"
    – antiduh
    Sep 9, 2014 at 21:17
  • @Tester101 - Thanks for looking out for me, but I've already looked into it. Rochester only has a single discharge system; sanitary and storm are one and the same. Plumbing code discourages sump discharge connections, but allows them. Unfortunately, because my property is so small, there is no place to discharge that wouldn't end up back in the house, or affecting someone else, or spewing all over the sidewalk and street. Half my property is uphill and is the exact source of the water I'm trying to remove. The other half is a 5-foot-wide sideyard. None-the-less, sump to sanitary is allowed.
    – antiduh
    Sep 10, 2014 at 16:39
  • 1
    What's wrong with "spewing" (or can we say flowing?) into the street? That's exactly what most sump pumps are designed to do. From there, into the combined sewers but avoiding all the problems of back flow, trapping and venting of a high pressure pump output. Could you run a pipe underground to the curb?
    – jay613
    May 8, 2023 at 14:46

2 Answers 2


Caveat: I'm not familiar with code for connecting a sump pump to sewer lines, so this answer is not authoritative. I'm taking a stab at an answer because most people in most places are experienced only with "never do that".

Where to connect: I would connect only to the main vertical line by adding another wye at the bottom or changing one of the wyes to a double one. The reason is you are forcing high volumes of water into the system. Any slight blockage or restriction in the flow could result in sump water being forced by the pump back into your sinks and toilets. Definitely don't join an existing 2 inch pipe.

In fact, you might even consider installing a main drain check valve near the bottom of your main riser and attaching the sump below (past) that. This would have the double benefit of protecting your home from inflow of storm water from the combined sewer system, and protecting your home from backflow of water from your sump pump.

Venting: If you need a trap, it's possible the sump pit itself could qualify. If you set the low-water mark (where the pump switches off) to be an inch higher than the water intake, that would act as a trap. I don't know if it's allowed but it would make sense. Venting this arrangement is an interesting problem. I wouldn't put an AAV too close to a powerful pump. Do you not have any standard through-the-roof vents you could connect to?


Just go up the wall to the top, put a single 90 across to a 45 that shoots into the wye where you connect it in the middle. Make sure you have some play with the line that's 2 inch or you will have to use some mechanical joints in order to make the connection. This is overall a simple and effective way of doing so.

Also, use all around to keep stuff nice and snugged up to prevent leaks. Be liberal with the glue as the pressures from pumps are high. Other then that solid setup and position too be in.

  • Use what all around?
    – isherwood
    Oct 5, 2023 at 16:09

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