I discovered this type of drip watering can thanks to a reel and found it truly ingenious! It works very simply: just immerse it in a container of water and it fills itself thanks to the displacement of air. It's a fascinating little physical phenomenon: air, just like any gas, takes up space, and when water takes its place, it pushes it out. Once full, all that's left to do is close the vent hole to trap the air inside and make it ready for use.