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Old 11-07-2010, 09:15 AM   #1
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P-trap for sump pump to stack connection?


I am installing a waterproofing/drainage system for my basement (retrofit) since I am in the process of finishing it. I set the sump pump near a vertical stack, and planned to tie into it with 2" pipe (off an existing horizontal line). I saw in the "code check plumbing" book that the discharge line should tie into the sewage line after a vertical lift, and directly. This could result in sewer gasses backing up into the sump pit, so that must be sealed and vented.
Unfortunately, the pit I purchased is not meant to be sealed (the lid has a large opening for 2" pipe and goes from the center of the lid to the edge). I will not be pumping out any sewage either- just runoff and water from condensation of my boiler. I was hoping to tie a P-trap to the existing horizontal line (vented), and tie the sump pump discharge there- preventing a back-up of sewer gas. Is this OK?

Thanks.

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Old 11-07-2010, 09:37 AM   #2
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P-trap for sump pump to stack connection?


storm water normally will not be tied into the sanitary sewer. That should be pumped outside of the building to a point that it will not reenter the structure. But to answer your question, I don't think it will work. The horizontal line is not vented, the p traps upstream are. You need to vent each trap to prevent siphonage, and even with a vent i think the volume of the pump will cause you to lose the trap seal. Either send the water outside or get the proper basin

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Old 11-07-2010, 09:40 AM   #3
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P-trap for sump pump to stack connection?


That set up of your seems pretty tricky...

I have not seen a PTrap with a sump set up before...

Maybe ask this question over on Terry Love's site.

JW
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Old 11-07-2010, 11:03 AM   #4
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P-trap for sump pump to stack connection?


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storm water normally will not be tied into the sanitary sewer. That should be pumped outside of the building to a point that it will not reenter the structure. But to answer your question, I don't think it will work. The horizontal line is not vented, the p traps upstream are. You need to vent each trap to prevent siphonage, and even with a vent i think the volume of the pump will cause you to lose the trap seal. Either send the water outside or get the proper basin

In my city (St. Louis) it is allowed, provided you have enough vertical lift to bring the discharge above grade. The stack is indeed vented. This set-up is 100 years old, and that's just how they did it.
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Old 11-07-2010, 11:06 AM   #5
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P-trap for sump pump to stack connection?


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Originally Posted by JohnFRWhipple View Post
That set up of your seems pretty tricky...

I have not seen a PTrap with a sump set up before...

Maybe ask this question over on Terry Love's site.

JW

Thanks for your reply. I will check out the site. As a temporary measure, after installing the sump pump I was discharging it vertically over an I-beam, and back down into a floor drain that was tied into the sewer line. I did not have any problems, so I suspect that I should be able to do the same at the stack. Obviously I don't want to leave a plastic tube draining into the floor of my finished basement.
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Old 11-07-2010, 11:51 AM   #6
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P-trap for sump pump to stack connection?


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In my city (St. Louis) it is allowed, provided you have enough vertical lift to bring the discharge above grade. The stack is indeed vented. This set-up is 100 years old, and that's just how they did it.
Most cities don't have combined storm/sanitary systems, because they don't want to treat stormwater the way they treat sewage. Also, in the event of heavy rains, the treatment areas can be overwhelmed by runoff which can cause the discharge of untreated sewage into a body of water. If it is allowed, great. Makes it a bit easier to get rid of the water. Also, vents protect traps, not drains. Your stack is going to be vented, and you can vent a trap on a stack (wet vent) if you meet requirements for it. However, you cannot wet vent on a horizontal drain, you'll absolutely need a vent for the trap.
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Old 11-13-2010, 09:12 AM   #7
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P-trap for sump pump to stack connection?


Thanks for your help everyone. I had the city inspector come and see the set-up. He agreed that adding a P-trap connected to the stack was the correct set-up here. The horizontal pipe is already vented... I guess I could have added pics to avouid all the confusion.... one day I will post all my work on this site.
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Old 11-13-2010, 09:22 PM   #8
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P-trap for sump pump to stack connection?


If you are installing a sump pump, would you not also be installing a check valve? That would be it's own trap, as sewer gases can't travel through the water that would always be in the vertical discharge pipe. And I've never heard of any municipality allowing that set up either but, I guess some are behind in logic. I bet the city workers are REALLY busy during a storm trying to get the overloaded sewer system flowing and all. Oh well.
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Old 11-14-2010, 06:22 AM   #9
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P-trap for sump pump to stack connection?


In addition, if sewer lines are overloaded, there can be backups into buildings particularly when plumbing fixtures and floor drains are in the basement.

St. Louis is on a river, no? The Mississippi River. Insufficiently treated sewage might be dumped there.
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Last edited by AllanJ; 11-14-2010 at 06:29 AM.
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Old 11-14-2010, 07:53 AM   #10
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P-trap for sump pump to stack connection?


Yes, thanks for your points. St. Louis is on a river... but there is only one sewer system in the city, so there is no separate way for the city to handle runoff water. So it all goes into the sewer anyway. That's why the city allows you to do this. That being said, most communities in the suburbs with newer serwer systems do NOT allow you to do this. St. Louis has 3 million people, but only 350K or so actually live within the small city confines... I will ask my neighbors if the sewer has ever backed up in the past 30-40 years, but I don't think it has. If it has, I will install a sewer check valve... but that can be pricey.

Plumber26's point is interesting- why install a P-trap when a check valve sorta does the same thing... I never really thought about that. Well, the inspector already saw my set-up, and agreed with the P-trap. But I could see it working fine this way too.
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Old 11-14-2010, 09:05 AM   #11
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P-trap for sump pump to stack connection?


the check valve that i believe plumber26 is talking about isn't for if the sewer ever backs up, it's to keep the vertical section of the outlet drain from draining back into the sump, so you only pump the water once. a swing check and full port ball/gate valve is required for any sump pump in my area, but i don't believe its a substitution for a trap in your configuration. basins that do that are fully sealed and cannot vent gasses, if something does make it into your basin you'll want some sort of protection from the gasses
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Old 11-14-2010, 10:11 AM   #12
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P-trap for sump pump to stack connection?


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Originally Posted by the_man View Post
the check valve that i believe plumber26 is talking about isn't for if the sewer ever backs up, it's to keep the vertical section of the outlet drain from draining back into the sump, so you only pump the water once. a swing check and full port ball/gate valve is required for any sump pump in my area, but i don't believe its a substitution for a trap in your configuration. basins that do that are fully sealed and cannot vent gasses, if something does make it into your basin you'll want some sort of protection from the gasses
No, I got that... there would be 2 separate check valves. The vertical pump check-valve IS required (although a ball valve is not). There are also sewer check valves that need to be installed for fixtures below manhole cover-level in case of sewer back up (in some areas- apparently not mine). These are a pain because they MUST be accessible, and some sewer lines (like mine) are below the floors... this would screw up all my plans... OK, not screw up but make WAY more expensive and painful.

In regards to gasses- there is no back-up of sewer gas in my system because of the P-trap (see title). I agree the potential pitfall here is the soil gasses.. the city DOES NOT require you to vent them. However, I am installing a vent from the perimiter drain to the outside for this very purpose. It just isn't near the sump pit.

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