Various systems are available that guarantee a good connection of CO2 tubing. High-pressure tubing can be connected with push fit connectors. The end of the tube is simply inserted into the opening of the connector, where it is held in place by small internal teeth. These connections are very stable and yet can be disconnected quite easily. More common screw connectors can be used with both high-pressure and silicone tubing.
For connecting CO2 tubing inside or onto the tank, stainless steel or glass tubes are available to keep the tubing straight that leads to the diffuser. This looks quite attractive, too. So-called U pipes make sure the tubing does not fold where it leads over the aquarium rim. J pipes fulfil the same purpose but are a bit longer, thus providing you with the possibility to connect a CO2 diffuser with as little tubing as possible.