Check valves for 1/2" or 3/4" Vinyl Tubing?

[Myka]

Can't help you on where to find one, although I would like to suggest that you design your system in way that you don't rely on check valves to keep your floor dry. Redundancy is key when coming up with a good design, so if you design the system so back flow is minimal (keep return lines high, use stand pipes in the overflow) and the sump has space for the back flow then check valves are a moot point, and you don't have to worry about failure.