"Please note, that there is no wildcard stop for fluids. This is intentional since fluids cannot mix in pipes."

There are multiple ways to make a fluid cleanup station. On the easier side, 12 pumps can be lined up to a single fluid wagon and controlled via the circuit network, so each one activates for a unique fluid, leading to 12 different tanks. On the harder side, a fluid sorter can be built for an unlimited number of fluids, and there are various blueprints online for this.

A wildcard signal for fluids would be very useful.

+1

or in modded versions, you could add fluid burners, and just burn off the fluids which somehow made its way there.

So:
+1

+1, hide it behind a setting if needed, would be very useful for SE/K2 where you can pump everything into a flare stack

I don't think a fluid wildcard is needed. In the mod settings under 'map' you can find "Depot Fluid removal Limit" for LTN. This sets a per wagon value for fluids to be destroyed when a train enters a depot.

Destroying items is a cheap workaround to a fun puzzle.