Enable manual Fluid IO from relevant UIs

[CreepTV]

TL;DR
I wish to be able to treat barrels as manually empty-able containers which can be filled and emptied from the UI of a tank/pipe/compatible machine.
WHAT?
So far we are only able to remove (read: entirely delete) the contents of a fluid network, but not add precise quantities without placing an assembly machine, set a recipe and wait for it to unbarrel a specific quantity of barrels. It'd be rather useful to either rid filled barrels without voiding them entirely or to kickstart certain production lines that rely on re-cycling or looping requirements (coal liquefaction in vanilla, many such cases in overhauls).
Perhaps change the UI element of fluids in a pipe to suggest that it could work like a spout or drain.
WHY?
Convenience and QoL, for the most part. Placing down an assembler/modded barreler, setting the recipe, inserting the item, etc. are all (relatively) long steps for a process that could be streamlined into the game engine.
Inspiration to this comes from the GregTech family of modded Minecraft, where manual fluid transport is done exactly as such, various containers such as cells, drums and barrels can be directly emptied and filled using the GUI of machines.

[Koub]

I'm not saying the idea is good or bad, but up to now, the devs have always favoured automation to manual labour. When a suggestion is aimed at making things easier to do by hand, the answer is usually no, whereas more automation has better odds.