Laundry sink pump s-trap?

[Herbie]

Here is the installation diagram from the manual for the Liberty 404 drain pump. It clearly states "Note: a trap shall be used between the fixture and pump, a flange type is recommended."

Will the s-trap be siphoned out, leaving the sink and washer stand pipe vulnerable to nasty pump basin smells? I can't figure out if the outside air vent on the side of the pump basin will somehow brake the siphon. Im thinking no, since the trap vent should be above the trap weir but the fact that its draining into a vented pump before being discharged into the sewer line is confusing me.

 

[Herbie]

Seems more logical to just inlet from the side with a standard p-trap arm. But why would Liberty go out of their way to suggest the s-trap in the diagram?

 

[Sponsor]

 

[wwhitney]

Seems more logical to just inlet from the side with a standard p-trap arm.

Agreed. Although that still raises the question of whether the trap arm needs to be vented before the pump.

But why would Liberty go out of their way to suggest the s-trap in the diagram?

Ignorance?

Cheers, Wayne

 

[Herbie]

Agreed. Although that still raises the question of whether the trap arm needs to be vented before the pump.

No. Pump is labeled for the side port as an inlet/vent and the adjoining top port as an inlet/vent (other top port obviously is discharge). So by using the side port with a p-trap, the top port becomes the vent.

Thanks for the reply. Its one of those puzzles where I was trying to make sense of the s- trap through the top, thought maybe I could learn something new.

I do appreciate humor if ignorance could be considered funny.