This is a simple indicator float for concrete water tanks.

A 25mm hole is cut in the lid, in this case a PVC access port. The sleeve is siliconed in. The float is put on the end of some 20mm PVC pipe and the indicator on the other end. Some silicone is added to stick them on.

It can be resized if you don't have 20mm PVC pipe.

The indicator can be printed in a bright colour to be easily seen.

Printed in PETC or ABS/ASA for UV resistance. Layer height, nozzle width and infill doesn't matter so much.