I’ve smoked out of plastic 2-liter GBs many times, all i’m saying is I’ve quit because its really not worth the risk, I assure you plastic toxins will dwarf ganja in damages towards your lungs.

however,

You can buy glass ones at your local headshop, or make one from some various alcohol bottles to DIY glass w/ a spare glass bong slide (for the bowl). All you have to do is file a straight fracture line around the circumference of the bottom of the bottle (which is easier if you make a tape line to guide you), submerge the bottle in a 5gal bucket of water, and knock the end off with a hammer. If you filed a good etch correctly, the break will be fairly clean, although sharp, but you could file it down or use a bead of clear silicone around the rim to fix that.
Use a rubber or silicone fitting of some kind (pen grips are convenient) to secure your bowl in the lid of the bottle, and you are good to go