It could be a bad wax ring. I would start by replacing that. also check the vent on the roof to see if it is clogged with anything
Get a one or two gallon bucket of water and pour it straight into your toilet. If the water goes down like a normal flush, your sewer line is fine and your toilet probably needs to be replaced or chemically treated.
Oh Yes, very common problem
some people flush their fish down the toilet when it dies, and the toilet is connected to the sewer.
It will more than likely plug the toilet and/or drain line and cause a flood and backup of the sewer
the toilet overflows if either the building sewer, branch line in your sewer system or trap in your toilet gets clogged.
Need to install a sewer pump to pump the sewer up to the sewer waste line
you most likely hve a bad seal at the wax ring.You did replace it when you replaced they toilet diden,t you?
the sewer
the sewer
it goes to the sewer
Your toilet waste should not be going anywhere near your sump pump ! Toilet waste is supposed to go down a sewer pipe to the street sewer or to your septic tank. No sump pump is involved unless you had a broken toilet pipe and you would definitely smell that.
Goes straight to sewer