by calculating the fixture unit requirements and the pitch of the piping for proper drainage
the toilet overflows if either the building sewer, branch line in your sewer system or trap in your toilet gets clogged.
yes
A compression flange is used to connect a toilet to the sewer line.
No you don't. The trap is inside the toilet.
5 inches of drop. 1/8 inch per foot.
I personally think the sewer line also your toilet water goes there.
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.
It will more than likely plug the toilet and/or drain line and cause a flood and backup of the sewer
It's called a CLEANOUT, and your sewer line is clogged.
some people flush their fish down the toilet when it dies, and the toilet is connected to the sewer.
Rubber gloves and a plastic contractors garbage bag
is is most certainly a blockage in the sewer line. Call a plumber to come and check it out and clean your sewer line for you.