i have a sump discharge pump in my basement for a sink and toilet installed 25 years ago. When draining the tub on the first floor that runs into the same waste line there is now a gurgling sound. I checked the pump and found it running while the tub was draining which it should not do. I figured the check valve failed so i replaced it and the problem is still there. I put my ear to the vent pipe and can hear water being pumped through it. How could the vent pipe suddenly be full of water and what should i do? We have had some torrential rains but this never happened before. Should i just try to drain the entire vent pipe by disconnecting it from the pump? thanks for any ideas.