Fredrick Maryland is experiencing severe flooding and one home owner has flood water gushing in the house through the toilet. You can view the video from the Facebook link above. What I don’t understand is how water can come backwards up the toilet? Aren’t there traps and other things that create suction or a seal? I’m not a plumber but I thought the pipes were designed to prevent something like this.
Best Answer
The trap on a toilet (or any plumbing fixture) prevents sewer gas from escaping. It's a very low-pressure thing, consisting solely of a small amount of standing water filling a low spot in the drain. Any force capable of moving a little water can overcome it, including air vacuum if it's not properly vented.
In the case of this flooding phenomenon, there must be a break in the city sewer line somewhere, and water standing above it. This obviously creates pressure that will escape at any point below its surface level.