That orange cap that is on the bottom was used for several brews 10+ years ago and I never had a problem with it coming off. The picture below shows what I used. That is a 1-3/8" OD diamond coated hole saw chucked into my Ryobi hand drill. The reddish cup is designed to help you keep your spot steady until you bite in, typically used for cutting ceramics. The cup is supposed to also hold water... but the surface has to be pretty dead flat, which the bottom of a glass carboy is certainly not. I just kept a cup of water handy and stopped whenever the work began to run dry. When I started back up each time I started slowly, slightly pulling the bit off of the glass and then built up speed in a few seconds. I really didn't push down and let the weight of the gun do the work, on high speed. It took about 10 minutes to cut through... and then about 5 more minutes trying to get the glass plug out of the inside! The bit and cup are sold together and can be bought at Lowe's/Home Depot in their tile tool section for about $30.