The principle of a vacuum brewer was to heat water in a lower vessel until expansion forced the contents through a narrow tube into an upper vessel containing ground coffee. When the lower vessel was empty and sufficient brewing time had elapsed, the heat was removed and the resulting vacuum would draw the brewed coffee back through a strainer into the lower chamber, from which it could be decanted. The Bauhaus interpretation of this device can be seen in Gerhard Marcks' Sintrax coffee maker of 1925.
Clean the inside of your machine by running water through it. Each machine will have a slightly different process, and some manufacturers provide tips and suggestions in user manuals. CoffeeLounge and other suggest mixing 2 oz. of vinegar in 20 oz. of water every now and then to clean out the machine even more thoroughly. After you use vinegar, though, be sure to rinse it three times with water to avoid any lingering vinegar taste in your next espresso.