[AllanJ]

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?

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.

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.