So much easier than a bung!
Rubber Carboy Blow Off Hood with two attachments for vinyl blow off hoses (3/8" or 1/2"). Fits our 3, 5, 6, or 6.5-gallon glass carboys with smooth necks. It can also be used on 5 and 6 gallon plastic carboys.
TIP: Carboy hoods are exceptionally useful for blowoff tubes. Just add 3' of 1/2" racking tubing into a bucket of water as your airlock.