Hey, so... yeah, the title already says it: the game can´t find a crafting recipe for the small inline storage tank, which makes quite a lot things uncraftable aswell. Not unplayable (yet^^)but things get so unnecessarily complicated that it´s not worth playing for now.

Might correlate with my Factorio being quite modded: all of Angel, AAI (except Containers&Warehouses) Bob´s, MadClown and py (except AlienLife) and some smaller ones which don´t mess with the gameplay that heavily that it would make sense to have an interference here (but can´t exclude them for sure).
(Well ok, to be fair FNEI does show me some crafting recipes since I have Revserse Factory installed, but these are the only recipes I get from FNEI and... if I can´t craft them at all, I can´t un-craft them, right?)

So the big question obviously is: does anyone have an idea what might have caused it? :)

I don't know the exact cause, but have heard about that recipe going missing when you have lots of mods installed. (Angels and AAI were mentioned previously to me)

Having Bobs, Angels, AAI and Py mods installed does tend to be a recipe for disaster though, when you throw that many mod packs together, small errors like this do creep in, and since you're dealing with 4 different people/teams, everyone ends up pointing fingers at each other.

All I know is, I add the recipe, and it should be available. Other mods change it (In this case, where it is unlocked), and if more than one tries to do that, since everybody is using their own mod library system (set of functions they call to perform tasks, rather than repeating the same code over and over again, one of the advantages to this is you can have the function perform more complex tasks like error checking, and it's still just one line of code to call it and perform the task), it's possible that when one mod moves it, then another tries to move it somewhere else, the unlock gets lost.

I know AAI's library for example has a system to find and remove an unlock, so it would get deleted even if it isn't on the technology his mod expects it to be, but if the technology he's trying to add it to doesn't exist (say for example, Angels deleted it), then it would get removed, but not re-added, leading to the current situation.

I'm not saying that is what is happening in this case, but that is a very likely scenario, given the ins and outs of how these mods change things. (and I barely know anything about the ins and outs of Angels and AAI, and know nothing about Py)

Thanks for the quick response, here are a few details I figured out in my desperate attempt to fix it by myself:

• A solution would be just to deactivate your mod (this one right here where we talk), so the storage tank don´t require the SIST (Small inline storage tank), everything else is craftable afaik and that´d be the end of it. But this is a problem of mine. I want all the mods (to enjoy Factorio to the max. And to live out my masochism idk^^) and I slowly start to realize to what cost my wish comes...
• I tried to deactivate all the other mods that the SIST had in it´s description a.k.a. AAI and some of py´s stuff, none of them changed a thing. Doesn´t has to say anything at all right now, but I figured I might add this info anyway :)
• A discovery that might prove your text about the find/remove unlock stuff: Whenever I tried switching mods on/off, I always create a new world to test this stuff. Nothing changed obviously, else we wouldn´t be here, but then I found out something irritating: one of these worlds that was a leftover from when I started modding Factorio actually does have the SIST aswell as it´s crafting recipe! It was found in the research "Electrolysis 1" which, by the looks of it, is one of Angel´s mods. I haven´t tried turning any of Angel´s mods off since I can´t tell for sure which one the culprit is (and I do not really like trial&error, esp. when each trial takes up about 20 min. in total), even tho it still may be worth a shot. And don´t even start me on why this is the only world where it works any why on every other world of mine the SIST recipe doesn´t work, I don´t know it :)

So that´s my status. Thanks again for the answer, I either will try a bit more on solving it myself, hope that some random stranger of the internet blesses me with his wisdom or I accept my defeat and start tuning down my Factorio...

In my own mods, The normal storage tank doesn't even cost the small one, the small one isn't an ingredient in anything, it's just a stepping stone, early game small tank, to make fluid handling a little easier when you first have to deal with oxygen and hydrogen from electrolysis.
It's one of the other mods, Angels I think, that changes the storage tank recipe to require my small tank.

Little update: I managed to nail it down to be pretty sure to assume that Angel´s Petrochem is the cause of all of it. The irony is that when you turn it off, the SIST has no use at all except being thrown into the void. And this is the point where my knowledge about modding ends. So either I go to Angel and annoy him/her with this or accept my defeat and adjust my game to it...

lmfao I did not thought it was this... simple.
So I wandered to Angel to check out if anyone beside me had the same problem as I do. From there I was led to the Factorio forum and hooray, people had the same problem. And the solution. The cause of error was PyCoalTouchedByAnAngel, specifically the DarkShadow44 patch I had installed. Deactivate it and behold, there is a working recipe for the SIST (the regular PyCoalTBAA by KingArthur causes no interference and can be installed just fine)!

So turns out I was just a greedy idiot who wanted to much, thanks for the help, case closed <3