Factorio Forums

When you are mixing two different fluids, "Cannot connect pipelines with different fluids" is supposed to tell you that you can't do that:
But no such error appears if the pipe is being placed directly on a building's output, despite the building's internal buffer being full of that fluid:
And if the pipes are super-forced-placed anyway (eg: by robots), no "Mixing fluid error" will show on the pipes that are right next to a building's output, even though those sure look like mixing fluids to me!

What I expected: Consistent behaviour if a pipe is placed next to a building, or next to a pipe is immediately taking a building's output: why do zero tiles of pipe cause it to not complain?

Save game: and log:

As far as i remember design decisions about fluid mixing checks, this is working as intended to allow for smoothie pipes.

https://www.factorio.com/blog/post/fff-442 - "Fluid mixing prevention"

Notably, fluid mixing only occurs on bidirectional connections; you can still create smoothie pipes by connecting pumps or unidirectional machine outputs with different fluids in them, and the game will not get in your way.

Ah, so this quirk is limited to one-directional connections: like a undirectional-output machine, which won't let fluid inside it. I see! Thanks for the explanation.