How big is the overflow?
You might try submerging a clear 2 liter soda bottle.
Cut off the top and the neck of the bottle, punch some holes in it and tie strings to rim of the bottle. If your clown hangs out at the surface like mine do when they're in the overflow, you can lift the bottle when she's at the top of the water and hope that when she swims down as you lift, into the bottle she goes.