For connecting your CO2 supplying equipment, you ought to use special high-pressure tubing for CO2, as these tubes are gas-tight and thus help keep CO2 losses down. High-pressure tubing made of polyurethane or LDPE is especially recommendable for this purpose. Polyurethane tubing is significantly more flexible than LDPE tubing. For connecting glassware CO2 equipment, you should use polyurethane tubing (if you want to use high-pressure tubing at all), however, you'll need to be extra careful when connecting it to the glass. Please make absolutely sure you heat the ends a bit before connecting to make them more bendable and to prevent glass breakage. In general, glassware CO2 equipment is better connected to the system with a softer and more flexible silicone tube to prevent it from breaking. Silicone tubing is not gas-tight, however, and thus only as little as possible ought to be used.