Pipe and Gas Bridges make them flow

It's a design choice and not a bug. "But it's not realistic" is not a bug.

Well. And i'm sure that it's a bug, not a design solution.
Cause you could build a lot of pipes around your base pumped all the liquid and gases in them and just destroyed every pump and valve. And all the system would work without any energy or temperature increase.
Cause if pipes a long enough and you build them with a good scheme you even don't need any sorts of automation. You could even kills germs inside of pipes.
Well you still needs a vent to prepare food, but thats all.

And what about buildings that have liquid output? They won't flow because there is no pump?

Currently, all output (green) can push into any connected input (white), this simplified logic that need to be handled for each tick. It is not realistic, but I believed they decide this with performance and extensibility in mind. Making something in the future that involving piped liquid, just put input/output in them and they will behave like the others without any extra piece of code.

If you mean Natural Gas Gen
it's reactions

CH4 + 2O2 = CO2 + 2H2O with complete combustion of pure material
+ N2 + O2 if material wasn't clean
and + CO + H + C if the material has not burnt out completely

So I think that this item also works incorrectly. Because should allocate steam, not dirty water.
And must work only in O2 atmosphere. Like other generators based on combustion of the material.
Cause you know. Science. =)
So if this water is actual steam it's just condensate near the Gen from time to time. Still doesn't understand why it's dirty. But ok let's think that material has not burnt out completely.

Also I think it's strange that such an advanced things like Gens does not have an exhaust pipe. In contrast to the previously studied water toilet.
And i think that if water toilet was builded without output pipes it's still should work but emits dirty water directly on floor. )
And all this stuff where output pipes wasn't connected must work the same way. But so far this does not affect the balance very much. So it's just my opinion that this should be more fun. =)

As for the complexity of calculations and code. The current mechanics can be completly transferred to a new explored object such as a pump that is slightly supplied with electricity to operate. And the bridges from the pipes are just counted as ordinary pipes.