Neat, now put it on the inlet side and you can catch sea
creatures.

Um, it's a thermostatically controlled open loop cooling system. The
raw water is circulated through the block, when operating temperature
is reached the thermostat opens and some water exits through the
exhaust elbow, and is replaced through a one way valve from the intake
through hull. The volume of water pumped through the block is
constant at a given RPM, and its temperature is constant. The
strainer is in the loop, just before the water pump, per the engine
manual specifications.

The amount of water entering and leaving the system is a function of
the surrounding water temperature and how hard the engine is working
(throttle setting).