They can do wet and dry pic up. These machines are very popular with building industry and food and printing industry. In the printing industry they use them to suck up excess ink and gulp from the printing machines.
You can only use it with two motors but then again why would you want only one motor, On a drum this size it would not move enough air out of the container to make sufficient vacuum.
I had a sl200 some years back and used to use it like a central vacuum in our old ( small ) house. I would leave it in the garage and run a 100 meter hose into the house and vacuum, aaah silent vacuuming 
