Sewage ejector and low flow toilet

I would like to replace the toilet in the basement bathroom with a low flow toilet but I think I may have a problem with the sewage ejector pump vent (or lack thereof).

We have a Hydromatic pump (circa 1975) which appears to have the vent cover removed. It's been this way for a long time and every once in awhile we have to pour some bleach in there to kill the smell. This usually happens if the basement bathroom hasn't been used in awhile.

I've attached a photo of the pump setup and you can see the cast iron ring has been removed and set to the side. Is there supposed to be some sort of vent here or do I just need to put the ring back on and seal it?

We also have some "extra" parts and I have no idea where those might go. You can see part of another cast iron ring in the foreground of the picture.

It's a full bathroom including sink and shower. We currently only use the toilet and sink.

Thanks for your comments and input.

A sewage basin must have a properly connected vent line to allow air in and out of the pit. Allowing it to vent indoors not only smells bad but could create gases that may be poisonous and/or flammable.