What does that plumbing valve do?

The most important part of a good home inspection is the education about the home.  Above and beyond the defects that good home inspectors will find, helping the new home owners understand the weird knobs and switches that are in a typical home is really where good inspectors earn their wage.

One type of knob in particular that I see often in more recently built homes is the "hose bib winterization valve."

It seems simple enough however they usually are not anywhere near the hose bib (outside water faucet)!

In a two-story home, these valves are usually stuffed under an upstairs bathroom sink.  The placement is good because if you shut the water off and open the bleed valve the water will readily drain out the outside water faucet.

If you have a recently built home and see one of these under the sink:

you now know what that weird thingy is for.