I have recently built this cyclone vacuum (second version) which drives a house central vacuum system. It uses 2 standard vacuums, is easy to construct and in normal use I estimate that the bin will need to be emptied every 4 - 5 years. The parts can be found in a hardware store. I have made a youtube video of it in action at
The earlier version let no dust get to the dust bags in the vacuum cleaners and this one is even better.