Had a new air handler put in the attic and I need to hook up the condensate drain. It is 3/4 PVC and has a P trap and tee's into the bathroom sink vent in the attic. The old PVC drain had a vent immediately behind the P trap which consisted of a T with a 6" piece of PVC glued in it. The vent was taped closed when I bought the house.

Is the vent needed? It's about an 8' run from the air handler to the sink vent with one 90* bend in the line and the P trap about 18" from the air handler. The way it was setup we never had a problem with sewer smell in the house or attic.