"Limey Lurker" wrote in
oups.com:

In commercial applications, I cut a
piece of 1-1/4" PVC drain pipe the length of which is the same as the
thickness of the counter top. I silicone that in place creating a
sleeve.

What is this for, please?

I'm surmising Rob does this to water seal the holes through which the water
supply lines pass. Clever trick which I may use next time.

Patriarch