A Check valve will only stop the liquid from flowing in one direction, and that would be from your tank and into the C02 mix, it would not stop the liquid from your C02 bottle getting into your tank.
You can make a cheap separator out of a small fizzy bottle.
http://www.aquaticplantcentral.com/foru ... xygen.html
Forth post down, the little bottle attached to the yeast bottle.
Use a drill bit the same size as the internal diameter of the air hose and force the airlines into the bottle - you can try to seal it with silicon but it may not be necessary.