The water level does not go down at all. Tenant says that everything else is working fine, sinks/washer etc. but did say showers backed up at one point. Breakers are fine and they have tried plunging and snaking. Any suggestions?

What happens when you flush? Toilet backs up and runs over? Water comes up the bowl, swirls around and then slowly goes down without taking the solids down? Please explain. Tom

It backs up but doesn't swirl at all. Thanks for your help.