If the pump does not work when there is water to be gotten rid of and you flip the switch then something is not good.I have a laundry room in my basement, I've used a laundry tray pump for the sink for a number of years. It is not always pumping out the water when I flip the switch. If I have a check valve installed, do I also need a trap on the sink? I've taken the pump apart and everything looks good. Any suggestions?
You need a trap somewhere between the sink drain and the sewer pipe exiting the house. If there is a holding tank where the pump resides then you need a trap between the sink drain and the holding tank. This is true with or without a check valve.