I just watched skye storme's hydrogen bubbler on this https://www.youtube.com/watch?v=v4sKlv081To&t=2560s and I must say I am pretty disappointed In real life, the hydrogen will quickly stop flowing once the pump is switched off and the gas/liquid inside the pipe reaches equilibrium.
Gases and liquids in pipes shouldn't behave any differently from gases and liquids in an enclosed space outside the pipes albeit in a much longer and smaller enclosed space. Water should still flow downhill. Poo water aka sewerage should still flow downhill. We don't need a pump. That's how it works in real life and in-game (when not in pipes), I don't see why gases and liquids should behave any differently just because they are in a different vessel call pipes rather than say two row of tiles that encloses said gases or liquids.
Follow Skye's design on the youtube link provided