DIY co2 inline diffuser & check valves

[nickdu]

I'm planning to build my own in line co2 diffuser and had a simple question.
I know that they are installed on the return line going back to tank. What i want to make sure i got correct is when the dieffuser is placed vertically in position, you want the water flow to go from top to bottom of it, right?

Also, i'm wondering if anyone knows good check valves out there to plug into co2 line that do not allow water to travel upward to the regulator w/ solenoid? The first one's i got failed after a short while. Any good brands out there? Can the solenoid get damaged from water?