- Flooding occurs when water and sewage from the toilet are not able to exit normally through the sewage and drainage system. Because the internal piping of a toilet is designed to prevent backups into the toilet itself to avoid potentially dangerous gases from entering the house through the sewage line, the water that has been flushed from the toilet follows the drainage line back to the open drain of the shower. This is most common in basement or ground-floor bathrooms.
- Flooding is almost always caused by a clog in the mainline of the drainage and sewage system. A small amount of flooding that drains relatively quickly indicates a small or partial clog that slows the water as it passes through but does not stop it in any significant amount. Long-term flooding that involves a large amount of water or that does not drain for several hours indicates a major clog that is able to block the flow of most of the water and sewage through the pipe.
- Clogs in the mainline must be cleared using a pipe snake or similar piece of equipment. If a clean-out access point exists in the mainline (indicated by a section of PVC pipe that comes out of the ground and features a removable end-cap), the pipe snake can be wound into the mainline from there and used to break up the clog. If no clean-out point exists, the pipe snake may need to be fed through a drain in the house, or the mainline may need to be exposed so that an access point can be added for future use. In most cases this clog removal is performed by a professional plumber, especially in cases where a clean-out point must be added to your mainline.
