I saw the thread in https://powdertoy.co.uk/Discussions/Thread/View.html?Thread=3643 but I did not want to necro it just because of the ambiguity of the OP, as well as having been posted 3 years ago.

I thought that, while it is admittedly not necessary for the development of the game, an option regarding communicating vessels could be a fairly good idea that people could switch on and off (just like ambient heat). It would improve some gameplay where pipe should not be needed (while I fully understand that many people may well be against this proposal).

Coding it will surely be a great difficulty, but since a sort of communicating vessels already happens if you add pressure to one of the vessels, this effect could be use to see how to solve the problem.

Any thoughts, ideas or comments?

I had not seen it! Thank you!!!