Add a raised loop up in the space outboard of the water pump, up where the purple hose is. No need for a vented loop. If the boat sinks 'that far' a vented loop is the least of your needs. Just raise the hose up so the top is a foot above the thru hull.
like this:
One of the problems with these bilge pumps installed like this is the hose drains back into the boat after it shuts off. Nothing like wanting a dry bilge then having the hose contents siphon back into the boat. The solution is to make a raised loop as close to the pump, so the amount of water that flows back into bilge is minimized. In your case I would consider installing the hose straight up from the pump on the FWD bulkhead, up to a loop and running it down and over to the thru hull to make as short a run to the loop, and have longest run after loop to thru hull. Make sure you have a constant downward slope in the side from the loop to the thru hull that way it drains completely and doesn't let algae grow in the hose to clog it up.
I wouldn't depend on a thru hull mounted checkvalve to stop water ingress. Checkvalves get gunked up with bilge scum. (although your bilges look pristine) Freely moving parts and seawater don't last long.