Installing laurdry/washer drain pump....

So ive piped to the tank that contains the pump, it will be draining a washing machine and laundry sink. The inlet and exit are 1 1/2. So i will vent to the stack vent, but the drain is where im unsure of the best course of action.
Should i ..
A. Pipe pump exit up and to the drain for the shower ? This is a 1 1/2 pipe

B. Pipe pump exit to the main trunk that is a 4 inch pipe? And then should there be an aditional gas trap if located in the drain? Or will the pump check valve serve this purpose?

The pump itself acts as the trap. The check valve just prevents backflow. And what do you mean by, "So i will vent to the stack vent", since from your description you may NOT have a "stack vent"?

The vent stack i have runs the 3 floors through the roof, the pump tank has a third location for a press in pipe for venting of the tank. Sorry "mords wixed" up
Thanks for the advice!

Ben D

Is that a "vent stack" or s "drain stack"? A "vent stack" would normally start about 4' above the floor on the lowest level and then go through the roof. A "drain stack" would run from the highest level down into the basement and then go to the city sewer. If you have a "drain stack" you CANNOT vent the pump to it, nor would you want to in case of a sewer backup which would flood the pump first, and then the basement.

Well i believe a vent stack. Tees off of the main trunk from the house (that goes to the septic tank) and goes up all the floors through the roof...not connected to anything other then the main house exit. It does start off as a 1.5 pipe then for the vertical it turns into a 2" pipe for the entire run...