system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why, no matter how much I pee, does the toilet never fill up?

I just peed a bunch and the water line just stayed the same!
gpt
The drain has a "U" bend so that if water is added to one side (like urine) the other side rises just as much and drains down into the sewer. This has the benefit of making a water "plug" that prevents sewer smells from coming back up the line to bother you.