I recently changed out a pump in a grey water sump basin located in the basement of my house right under my kitchen. I had what I think was a standard sump pump in the basin with a 1.5" discharge, but no numbers or name so I have no idea on hp or gph. I replaced it with a Wayne EFL30 .3hp effluent pump. I now have a gurgling in the kitchen sink when the pump below starts (they use the same 1.5" drain pipe from the sink) and when the pumps stops, I have gurgling again and some water backing up into the sink. I thought it might be a partially clogged pipe, but the water does not back up until the pump stops. When my clothes washer is draining into the basin and the pump is running there is no noise or water backup. I also checked the kitchen trap and it appears the water there is getting pushed up the tailpipe when the gurgling occurs. I did not have anything like this when the sump pump was in, but that has a built in pressure switch that is failing and I cannot replace the part, so I had to replace the pump.
Any ideas/thoughts would be helpful.

Describe your drain and vent piping from the kitchen sink to the main drain.

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.3hp effluent pump

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Is that .3 hp or 3 hp?

The sink drain (1.5" copper) goes into the wall under the sink, then down the wall and out overhead in the basement. Effluent pump enters the main drain line about 2' after the sink line comes out of the wall overhead in the basement. The vent is in the wall where the drain enters under the sink, but I am not sure how and where it connects into the drain. It is not directly over the drain pipe entrance into the wall as there is a window there. It has to move over about 3 feet before being able to go out the roof. There is a 25' run across the basement until the line drops about 4' into a 3" line to the sewer.
The pump is 1/3 horsepower pushing about 3900 gph at 0' and 2900 gph at 10' where it connects to the overhead drain line. Volumes according the manuf website.
Steve

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line drops about 4' into a 3" line to the sewer

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Is that 3" line vertical or horizontal?

3" line is horizontal.

Suspect you have a partial blockage or restriction in the 3" line.

Try this logic, see if it fits.
Assuming the pump line intersects with the kitchen drain with "Y" or a TY (sanitary fitting).
You nave a partial blockage in the 3" main. When pump comes on, air in the kitchen drain is forced out causing the sink trap to gurgle. While pump is running, water from the pump is under pressure, directed toward the 3" line. Back pressure will cause some water to move toward the sink and up the drain line. But not enough to cause the water to reach the sink. Some water passes the restriction in the 3" line but some flows into the horizontal line and upward where it turns vertical. Makes sense to me that the level in the 3" vertical line could be higher than the level in the kitchen drain because of the force of the water being pumped in that direction.
When pump stops, the higher level of water in the 3" line causes level of water in the kitchen drain line to rise and enter the sink.

Presumably, the 3" line comes from a toilet and other fixtures on upper floors. The volume is probably less than the volume from the pump and the restriction or partial blockage is not severe enough to to cause a problem. The partial blockage is probably some distance from the upper floor toilet and other appliances, and the 3" line is large enough and long enough to temporarily hold enough volume for you to not notice.


To test this logic, flush toilets and run water in the fixtures that are served by the 3" line while pump is running. If logic is correct the amount of water backing up in sink will increase when pump is turned off.

Or, just snake the 3" line.

The 3" line is about 4' below the 1.5" line coming off the sink and pump but it makes sense, There is a clean out easily accessible off the 3" where the connection between the 2 pipe sizes happens so I will try and snake the 3" line.
Thanks