I've gotten as far as causing the fountain to create source, the only problem is it creates it underneath it and not around the tap like the base game does.
I see that the source fountains have a trigger around the tap but i can't find any reference to a script nor can i find any script like it
How the fuck do these things work?!

You could use a goal in the story editor to achieve it. The following code is a very basic example that'd spawn a Source pool with a 1.6 radius from its center for a -1.0 lifetime (infinite), where you'd have to replace {ITEMGUID_Fountain} with your fountain item's ITEMGUID.

IF
CharacterUsedItem(_Player, {ITEMGUID_Fountain})
THEN
CreateSurface({ITEMGUID_Fountain}, "SurfaceSource", 1.6, -1.0);


If you'd want to make the surface appear off-center, you could perhaps make an invisible helper or pointtrigger and replace the CreateSurface call with CreateSurface({Point trigger ITEMGUID / Helper ITEMGUID}, "SurfaceSource", 1.6, -1.0);

If you really want to get into modding then I would recommend considering to join the Larian Discord and hop into the modding section there