I recently purchased a house that has a finished basement. The new basement includes a full bathroom. A lift station was installed underneath the vanity to accomodate the new fixtures. From what I can see is the top of a 55 gallon drum that collects the sink, toilet, and shower waste through pipes that I assume run into the side of the tank. The tank has been set into the floor. On the top there are two pipes coming out of the lid. One is the sewage exit line with a backflow fitting and the other is a vent. I recently had family visiting that used the bathroom during their stay. Since they left, there has been a sewage smell coming from the tank. When I flush the toilet, I can hear the pump come on but it only comes on for a few seconds.

What can I do to fix the problem? It doesnt look like the lid is sealed to the top of the tank. Both of the pipes coming out of the tank have rubber compression fittings which I could losen to take the lid off? Is there some type of addative I can add to help this and does this seem to be a typical type of installation? I recently added Rid-X typically used in septic tanks. Could the long times between use without visitors cause a problem? Any advice would be appreciated!