The toilet and sink in one of my bathrooms was working fine. Then the toilet got to where it gave a poor flush like it was having trouble going down. I them took a plunger to it to get it moving. All I did was move sewage into the bath tub. When I try to use the sink it bubbles up in the toilet. The other batroom still works just fine. I want the first bath to drain but do want to compound my problem. Where to start?