A filter I made for when I'm cleaning my aquarium. A hose (17mm) is inserted in the filter and while the water is drained from the aquarium I'm stirring up the gravel in the bottom and let the sludge be sucked up and out.
Secondly when fresh water is refilled into the aquarium via the hose the filter helps disperse the water stream.

The included STL file fits a hose with a diameter of 17mm but I've included a Fusion 360 design file for anyone who want to tinker with sizes and dimensions..