Do you need a check valve?
This is my first time setting up a co2 system for an aquarium and I decided to set up a DIY system using 2L soda bottles, citric acid, and baking soda. I have all the standard supplies such as a bubble counter and diffuser, but I forgot to get a check valve. I heard that you dont need a check valve as long as your system is above the aquarium. I dont really understand the concept of back flow/siphoning as I thought that even if water were to back flow how would it get on the ground as it would be trapped in the tubing connecting the the regulator to the diffuser. Even though I dont really understand the process of back flow, I still want to be safe, so when talking about the system being above the aquarium, would the entire 2L bottles and regulator need to be above the aquarium, or just the the regulator part where the tubing is coming out of. If anyone has any of their own DIY setups with no check valves I would appreciate it if you could send me a picture to help me better understand the process.