Basement bath - septic tank gas!

[jkcal436]

I have a full bath in my basement (installed by the owner that had the house before me). We do not use this bath often (maybe once a week). But, when we do the septic tank gas comes in and is bad! We have to run the water and flush the toilet again to get the pump to come back on and create a seal. I believe that the septic tank is above or on the same level as the septic tank. The gas lingers for a couple hours. Any fix to this? Is this a serious problem...other than the gas being flamable and hard on the nose?

[AllanJ]

Is the toilet outlet and also the sewage ejector system properly vented to the outside? This is needed to get makeup air during ejection as well as allow gas from decomposing sewage to depressurize. During normal use of all fixtures the toilet bowl and the sink and tub traps should not be sucked dry otherwise you have a vent problem. Also be sure that the lid of the ejector system is properly secured.