When my pond pump is switched off the natural siphoning action draws water, and any nearby gravel etc, 'upstream' to the lower inlet pond via the impellor housing, This thing is designed to prevent the ingress of any foreign matter into the pump. Suits a 25 mm hose. Has the added benefit of creating a nice laminar flow ... Change the parameters in OpenSCAD to suit your own installation.

Printed on a Replicator 1 using 1.70 mm ABS at 100% infill (watertight ...) with 0.2 mm layer thickness and 120 mm/s feed rate (go Sailfish!). Print with the base flush with the build plate. Enjoy!