It's been tested.
The strangest thing happened...
I cannot blow through it in the opposing direction, but the CO2 can penetrate the valve.
This morning I specifically checked this, because I hooked up my canister (Magnum 350) as a reactor and wanted to see if it would work.
(Mind you the canister is a temporary solution until I purchase a powerhead. The only thing in the canister is an empty media basket.
It seems to be working just fine as a reactor, for the time being. I know I'll have to occassionally refill it with water as the gas displaces it.)
Anyway, there are most definitely CO2 bubbles coming from the solution and entering the canister.
I can see them at both locations.
Now I'm not sure what to make of this.
Perhaps I still need to replace the check valve.