Prevent the Loss of Volatile Solvents in Rotary Evaporators with a Simple Device, Daan van Leusen, Journal of Chemical Education, 1994, 71 (1), pp. 54-55. D!
One of the regular readers just emailed me a picture with a similar set-up to mine that does the same trick (See comments and picture right). The main difference is that this alternative set-up doesn't allow you to turn the vacuum off by turning the tap. Were I work we have a house vacuum system that requires a lot of tap turning so the set-up above is nice as this simplifies turning the vacuum off. However, if you are using a diaphragm pump this alternative is perfect and presumably also significantly cheaper to produce. D!