Check valve to block mosquitos?

[sodamo]

Panty hose - best prefilter I’ve found. Cheap and effective. We live off catchment water. A panty hose filter is part of the filtration before the tanks. Filter down to 1 micron after tank and before UV. Can post more detail if any interest.

 

[MillWeld]

Neal, that's even easier. Thanks.
Bob

 

[dstig1]

If it is 4" dia, perhaps a dryer vent hood with flapper would do the trick. Cheap as dirt and easy to find. Slip over pipe and hose clamp it on.

 

[jaxs]

Why not just cut the end of the pipe on a 45, then hinge a piece of sheet metal at the top. Weight would keep it closed until water pushed it up.

That's so clever and simple I should have thought of it first.