There are multiple methods, with the most common being to score around the glass and then snap where it’s been scored. The break should follow the scoring, but you will want to be careful and hold it inside something like a towel or rag to protect you from any fragments or glass dust. If you don’t have a proper glass tubing cutter, it’s possible to do this with a triangular file. Proper tools are of course recommended and will have a better success rate. You'll also want a high quality mask to protect your lungs, and doing this process while wet will help reduce airborne glass particles.
