Hi, folks. My toilet has an issue where it constantly filling the toilet bowl from the tank, causing it to refill a half inch in the tank every 15 minutes or so. I figured out that this orange rubber ring has gone soft and warped and needs to be replaced because it's not holding a seal. Thing is, I don't know what that's called. It takes up the spot that would normally be occupied by a flapper, but it seems to be a different mechanism.

I tried to remove it but there is a piece that extends through that pipe into the exit hole that prevents that. I'm sure I can figure out how to do the repair, I just need to know what to actually type into google/youtube. Thanks.