No need to seal it. The first thing to do when the pipe under the toilet returns water is to quickly inform all the residents upstairs not to use water for the time being. If there is no water upstairs, the backflow of water will stop.

But that doesn't mean everything is fine. Then, you should go in immediately and do the second step, that is, find someone to clean it up immediately. When the water flows back and the sewer pipe is blocked, you must find a professional dredge to deal with it. After dredging, we will inform all the residents upstairs to start using it.