A friend of mine managed to break an intake cover on his pool while trying to unclog one of the buried pipes.  After coming up empty trying to find a replacement, he gave me the pieces and asked if I could knock together a printed replacement.  This is the result.  It mostly duplicates the design of the original, except that the screw holes aren't countersunk.  (I didn't notice that on the original because I had the pieces upside-down on my desk as I was working on the design.)

Printed on my Hypercube 300 in 3D Solutech beige PLA, with mostly default settings in PrusaSlicer (0.2 mm layer height) except for these: 25% infill, Archimedean chords bottom layer, 0.75 mm first-layer extrusion width.

OpenSCAD source included, which might serve as a basis for adapting the design to different configurations as needed.

Update: it works!  Photo attached.