Basement Sink Pump Question

[pprobus]

A question about tying in a basement sink pump.  Where I connect to the DWV stack (I will be tying in on the vertical stack from the upper to lower level) is it recommended to put in a p-trap to keep sewer gases from going back to the pump?  When I searched for other installation recommendations, I came across an article from Popular Mechanics that shows them tying into the stack with no p-trap.  Since its not really any more work to install a p-trap while I am tying into the main stack, I figure I'd do it now and not, potentially, regret it later.

Thanks,
Paul

[Herb G]

Mine doesn't have one on it. Just at the bottom of the sink.
It does have a back flow preventer inline on the waste side of it though.

So, the sewer gas (if any) is prevented from going back into the pump, and rises thru the stack.

[MstrCarpenter]

Even though it's only for a sink, it is still basically a sewage ejection system. Here's my opinion based on several laundry and full bath pump systems I've done over the years. You shouldn't put a "p trap" on the discharge, and because the pumps move water quickly, it should tie into the existing stack with a wye. Your tank has to be properly vented, and in some instances, wet venting does not meet code. I did have a problem with odor on one of the box store laundry sink/pump set-ups. I put a P-trap on the tailstock, and a Studor valve (air admittance valve/vent) on the riser. The discharge got the check valve (which would definitely stop sewer gases) and then the tank top was sealed screwed shut. I thought everything was covered, it worked great for months; it just took a few months for the tank water to develop an odor. The problem was that while the Studor valve let in air to replace the water being pumped out, there was no provision to let the air being displaced by water going down the drain out of the tank. The slightly pressurized air would leak past the rubber grommets or occasionally burp in the trap. The only way to fix the problem was to actually follow the codes and vent to "atmospheric pressure".  I would have to connect the vent to the existing stack above the flood level of the highest fixture the stack serves or, as I did, add a new vent.

[pprobus]

Even though it's only for a sink, it is still basically a sewage ejection system. Here's my opinion based on several laundry and full bath pump systems I've done over the years. You shouldn't put a "p trap" on the discharge, and because the pumps move water quickly, it should tie into the existing stack with a wye. Your tank has to be properly vented, and in some instances, wet venting does not meet code. I did have a problem with odor on one of the box store laundry sink/pump set-ups. I put a P-trap on the tailstock, and a Studor valve (air admittance valve/vent) on the riser. The discharge got the check valve (which would definitely stop sewer gases) and then the tank top was sealed screwed shut. I thought everything was covered, it worked great for months; it just took a few months for the tank water to develop an odor. The problem was that while the Studor valve let in air to replace the water being pumped out, there was no provision to let the air being displaced by water going down the drain out of the tank. The slightly pressurized air would leak past the rubber grommets or occasionally burp in the trap. The only way to fix the problem was to actually follow the codes and vent to "atmospheric pressure".  I would have to connect the vent to the existing stack above the flood level of the highest fixture the stack serves or, as I did, add a new vent.

Thanks for all that.  Its good to learn from others experience.  I guess I should have anticipated not need a trap in the line as the line will be vertical for ~6' - 7' or so, the line will be full of water and not be able to allow sewer gas back into the pump.
(DUH!, brain fart on my end).  Yeah, venting, I was originally going to go with an AAV, but seeing what you have to do to do so (Studor put out a design manual), I don't have 6' of horizontal sanitary line to tie into downstream from the closest point I could tie the pump discharge into the sanitary.  Not to mention that point I'd be forced to tie into the discharge just happens to be over ductwork, making being able to cut out the elbow to install a Tee and then run the line to that point.  So, the easiest tie-in point is in the vertical stack that transitions from the upper level to the lower level although it will be a slightly longer run.  The venting I will either be able to run it behind the master bath shower into the attic and tie-in in the attic (doable but a long route), or I am hoping to be able to pull out the recessed medicine cabinet and be able to access the venting for both bathrooms through the hole in the wall (both located in the upper level, so tying in there will put me well above the flood level of all fixtures) in the smaller 3/4 bathroom and tie in there, since I don't really like working in the attic. 

Paul

---

Mine doesn't have one on it. Just at the bottom of the sink.
It does have a back flow preventer inline on the waste side of it though.

So, the sewer gas (if any) is prevented from going back into the pump, and rises thru the stack.

Yep, had a brain fart, over thinking things.  

[crokett™]

When I installed a pump in my basement for a washing machine I put a p-trap between the washer and the pump. I did not have a trap after the pump on the ejection side. I did have a check-valve. My pump was tied into the main vent stack.

[Terry W]

I'm currently in the middle of the same project, putting a sink & dishwasher in our basement bar area. After hours of research on AAV's I read the writing on the wall and spend a 1/2 day running a vent stack up from the basement, through a closet on the main floor and into the attic. In the attic I had to run it another 25 ft to an existing vent. It as a pain in the @#$$ but I'm glad I did it.

I was wondering about the P trap too, but as you have already figured out, no need as the check valve plus the pipe full of discharge will keep the sewer gas at bay.

Even though my pump/basin specs a 1.5" discharge, some spec a 2". I went ahead and piped in the standard 2" to the larger drain in the ceiling. I'll use a reducer at the pump for this one but if the next pump (10-15 years down the road) specs a 2" then it's ready to go.


Also, if this is new construction, don't forget to put in an AC outlet for the pump under the sink.

Good luck.