I recently saw a plumbing setup where a 2" pipe was run from a bend in the 4" toilet return. The 2" pipe bent upwards to meet the floor next to the toilet, where it was capped off with a removable cover.
In case of a clog, apparently the plumber uncaps and pushes air (or water?) through this pipe (or vent? valve?) to purge the clog.
First of all, what is the correct terminology for this apparatus?
And I hope it's not outside of the scope of the question to also ask does this thing function as a vent?
Will it have a one-way valve to prevent the elevated water in the toilet from rushing out when it's uncapped? (cap is level with the floor next to the toilet)
Here's an ugly sketch of the thing: