Popular Ozonator check valve made by Prozone with a 1/4" barb on each side. Manufactured out of a durable Viton material for years of trouble free service. The purpose of this check valve is to prevent water from backing up into your ozonator. It should only allows the gases to flow out of the ozonator, no water in. If your ozonator is leaking this part is the culprit and a very easy change. May come in other colors than what is shown in pics.

Pro Tip: When installing your check valve blow into each side so you can verify the direction of your flow which is away from the ozonator, back into the spas plumbing.