Ejector pit smell

I live in a 30+ year old ranch house. I was told by the plumber that the whole houses upper level bath and kitchen and my new basement bath are running into one ejector pit. The problem I have is when we fill up the bath tub upstairs and release the water, we get a bad smell from the ejector pit. The pit has a metal top but not 100% sealed since I have to access it now and then. I wanted to know if I can use some chemicals or cleaners to stop the smell? If not can I purchase some air tight top, that can be removed time to time? Any advice would be greatly appreciated.

ChiDude said:

I was told by the plumber that the whole houses upper level bath and kitchen and my new basement bath are running into one ejector pit ...

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... and what did s/he say about its top?

A sewage pit must be sealed, and you will find yourself opening it less after convincing everyone to never flush anything that has not already been eaten.