Lots of options in this thread. I do what MCKBrew suggested, however, instead of using that small tubing I slide a 1 inch tube right inside the airlock - fits perfect. I pour some starsan solution around the tube in the airlock and put the other end of the tube in a bucket of starsan solution. Make sure you cut off the plastic "X" on the bottom of the airlock so the blow off can flow.
Alternatively, put some Fermcap S in the fermenter and you shouldn't need a blow off tube