My downstairs washroom backed up. The toilet, the sink, and the shower. I don't even use that shower 'cause it wasn't built correctly...my brother had his stuff stored in it (HA HA!), but it backed up 2 inches. It also came up through the drain in the floor, which (brilliantly) has wood flooring over it. Am I correct to assume that this is grey water, and I'm going to have to cut out walls and replace the entire floor?