I have two – called 'WAP' and now I think Karcher – both nearly 30 years old. They are a square, boxy shape , about 600mm tall, about 450mm square. They use a circular drum style pleated filter, but can also use bags. I don't use bags since I use the cleaner to suck up all the mill and lathe shavings, oil n all, all the sawdust from wood machines, etc, and the bags just tear or abrade through and then the stuff goes in the motor.
I just slip a ladies leg hose/stocking over the pleated filter, and every now and then pull it off and shake out or replace. I clean the pleated filter maybe every 3 months – wash it out under the tap and leave to dry.
The machines have a good powerful motor, and I have not have to repair anything on either , and obtained them used from WAP way back… Hose is about 50mm diameter to, which is very nice.
Joe