The way I solved that problem, as well as providing a fool proof anti-siphon device, was to Tee off the raw going into the elbow with a smaller, in my case a 1/4 inch line and route it high up into my port locker and back down to the floor of the cockpit through the locker wall and emptying into a scupper. When the engine starts you can immediately see the water flow. If it stops, and that did happen to me a couple of years ago, exhaust smoke is immediately visible! Stop the engine and investigate! Impeller had lost a couple of fins. When you stop the engine normally you can hear the line drain and air flow.

Eddie