This is a set of parts to turn a PET or glass bottle into a watering station for pets. It works by letting air into the bottle only when the water level in the bowl has dropped, thereby automatically refilling. The CAD files are on Onshape: https://cad.onshape.com/documents/f916c31e5ee7e23ab42c4134/w/b839c7c1ca4c1f50118f40f9/e/ecd4bec31f2578c91f403fc2