So, I’m not sure how I can explain it. Basically, I want a script, or pack, or something like that to make a static mesh behave like water: when something drops inside it, instead of holding it up, the object being dropped will slowly sink to the bottom, almost ignoring the collision. Would there be any FREE way of applying this kind of effect on an object?
I’ve tried voyaging Google, but, either because of the inability to clearly ask this question or the actual lack of answers, I’ve found nothin’ useful. 
Sounds like you want to use a Physics Volume - check out https://docs.unrealengine.com/en-us/Engine/Actors/Volumes/PhysicsVolumeDetails
Mark it as containing water then that should be what you’re after. I think there’s a few tutorials for this kicking around. Can’t help much more than that I’m afraid - I’m new to Unreal myself having moved from Unity.
Cheers,