Weird Valves Under the Sink

Here are two small vial-type things, with caps, worked into the wall near plumbing pipes.  I have seen these curious things under pedestal sinks, and today there was also one under the toilet.  These have been spotted in newish homes (less than 20 years old).  I have no clue what function they serve, nor does anyone else I have talked to. 

All I can say is, they are darned hard to wallpaper around!!

Tags: pedestal sink, wallpaper