We just moved from California to Spokane Washington. We have never had a house with a Basement. Our house is only a year old. We have a furnace room with a floor drain in the floor. The drain is vented. Next to the drain the is a irregatioin box with a 3" pvc pipe coming up from the ground. Pipe is open but there is a flapper down in side, I think that what it is. Is this a check valve to stop sewage from backing up through the drains and bathroom fixtures. And should I have a sump pump installed for future issue if this overflows. Thanks Mike