More realistic water pipes

[BlueOrange]

When there's not enough water to fill a pipe completely, pipe contents should follow gravity (go downwards).  It should be possible to create a water inlet that isn't a pump, which will cause water to fall until it reaches something that makes it stop.

Why yes, I do want to install a gravity-fed shower, like the one on the farm when I was a kid (and save on energy costs).

[LeadfootSlim]

100% agree on a passive inlet or drain, because it's an absurd amount of work to build and power a pump to drain a higher-up pool to a lower one, and it feels unintuitive at times to dig a ladder and drip water down it to a lower reservoir.