Sump pump vents/syphons toilet

[mellow8]

I have a Zoeller 267 ejection pump in a basin in the basement that can be used for sewage but is only used for the washing machine (second bathroom never put in). It is installed IAW manufacturers instructions and has a DOM of 11-99. I have a septic system. I have lived here for about 2 and 1/2 years. The last 6 months when the sump pump runs while doing laundry bubbles appear in the upstairs (main floor) toilet and it syphons water out of the toilet. I cleaned out the pit and remove alot of lint out of basin and off pump. I checked and cleaned the check value which is very rusty. I have snake the main 4" pipe to the septic tank and flushed with garden hose. I have snaked both the roof vent and the vent on the tank to the outside. The problem continues can anyone help me figure out what is causing this. Do I need a professional pipe cleaning or what?

[cacher_chick]

Hard to say without knowing how the vent is hooked in.

The sump vent should be dedicated or else tee'd into the main stack in the attic. Wet venting between floors is not a proper install.

[mellow8]

The ejection pump has its own direct vent to the outside which is about 8' away. It is a 2" vent pipe that turns 90 degrees down after it reaches the outside I assume to keep rain out. The installation is as shown in the Zoeller instruction manual. The horizontal 4" drain pipe from the toilet and stack V into the 4" waste pipe after the tie in for the ejection pump about 10' from outside wall on opposite side of basement and about 14 ' from septic tank.I also forgot to mention that when I cleaned out the basin I made sure the 3/16 hole above pump and under lid was clear.