Good write-up. I like his write-up on check valves (well video) too. Brings the cost down from $10 to $2
http://www.instructables.com/id/How-To-Make-A-PVC-Water-Air-Vacuum-Pump/
Check valve one is here
http://www.instructables.com/id/How-To-Make-a-One-Way-Check-Valve-For-Cheap/