I think the rear sprayer on his car are powered by same air used by the horn, so the air going thru the hose blow over another hose connected to it, often at a flat angle in the direction of the air, this mean the rushing air will suck up some water thru that other hose that go to a reservoir of some sort.
On ships, for instance for draining the anchor chain storage "room" you use the fire fighting water system, as you already have that going to spray mud off the anchor chain as you retrieve it.
I also remember my chemistry teacher in school making a vacuum the same way with water from a regular tap, so the rushing water pulled air out of a confined space and so created a vacuum, making various air filled things like some candies swell up as vacuum was applied.
Also making luke warm water boil at temperature much lower than it would if there was no vacuum..
Actually this is the same principle in a ships fresh water generator, boil salt water in a vacuum, using hot but of course not boiling engine cooling water for heat to make salt water evaporate in a vacuum, and then you collect the fresh water at the top / sides and eject the brine that collect at the bottom.