We have been thinking about that for years but here would have the additional issue of freeze protection. My concern is that they wouldn't vacuum first and might clog the nozzle or it would get large "items" in the dirt water. I bet one of those would do well if it worked good and was priced just right.
I thought about mounting the whole thing, extractor, dirty water barrel, and a vacuum, all on a cart to be unhooked and moved out of the bay Friday night. I'd probably
lock the unit to the wall, and my original thought was to either roll the unit into the equipment room or build a storage for it, but I could
lock it to the back of the ER and hook it up there for weekend use. It just won't be in the shade.
My cousin used to have a bunch of washes, and he had a couple extractors with a vacuum next to it, and instructions to vacuum first. If they didn't vacuum, it wouldn't cause a problem with the machine, and the slit for pulling up the water was too narrow to let anything into the extractor tank.