Normally when you press down on the flush handle of a toilet, you expect the waste inside to be expelled quickly into the sewer drain. But if your toilet keeps backing up while flushing, the toilet might have a problem.
There are a couple of different places where a toilet could be backed up: inside the toilet drain or at the main sewer line for your house.
What Happens During a Flush
Pressing down on a flush handle in a toilet lifts up the flapper inside the tank. Once open, the flapper lets the water inside the tank rush out and into the toilet bowl.
The water swirls into the toilet bowl through holes in the lip of the bowl. This swirling action helps carry off the sewage inside the bowl into the toilet drainpipe.
The sewage in the toilet drainpipe then connects to the sewer main for your house.
Checking the Plumbing
The first thing to check if your toilet is backing up while flushing is the status of the rest of the plumbing fixtures in your house. When you run the shower, for example, does the water back up in the bathtub? Or does the water back up in the sink? If so, the sewer main may be backed up.
If not, the problem is with the toilet drain.
Clearing the Toilet Drain
Insert a plunger into the toilet and place it directly over the outlet. Press swiftly up and down on the plunger to help push anything that might be trapped inside into the main drain.
If this doesn't work, insert a plumbing snake into the toilet. Continue pushing it through the toilet drain until you feel it hit the obstruction.
Lock the snake extension in place by tightening the screw on the front of the snake and turn the handle to rotate the end of the snake in place to help break up the clog. Flush the toilet and check how it is draining.
If the problem persists, continue with the snake.
Clearing the Sewer Main
A backed-up sewer main can be cleared by the DIYer with the right tools. Find the cleanout plugs, which are circular plugs near the house or where the front yard meets the street.
Loosen the plugs on top with a wrench. Rent an electric snake and run the snake through the sewer main toward the house.
When you feel the obstruction, back up the snake a foot or so and try to power through. Continue until you feel the obstruction give way.