Replacing basement sink pump

kornfein

I am replacing my 20 year old basement sink pump that failed. The old pump was a box on the floor that pumped the waste water from the sink about 6 feet up to house drainage line. The old pump contained had an open copper pipe air that went from the pump box up the side of the sink and ended in a u shape into the sink, this pipe let air in and out of the pump. The new pump is similar in design except it includes a 1.5" hole for what it says is a vent pipe. I'm not sure what to do with it. I don't believe I'm anywhere near the house venting system pipes and I'm not sure what purpose it would serve hooking it up to that. There is a check valve upstream from the pump so it is not like water can back into the pump or sink. One other question, the old set up did not have a trap, the pictures in the installation manual show one so I'm inclined to add one any reason i should not?