Whenever I make a domain for a fluid and I rotate it, I bake it and the fluid just falls down as if the box is not rotated, I want to make it so it falls onto a rectangle ramp and slides down it but it just falls as if inside a perfectly straight rectangle…
If want to something similar to the vid below.
Then use obstacles within the domain just add a mesh and in fluid choose obstacle.
That way you may use the mesh or meshes to “guide” the fluids the way you want it to flow. If you already have e.g a ramp you intend the fluid to run down from use that as an obstacle. It will show in the render aswell in the video below though I choosed to have it hidden.
Anyway I hope I understood you correctly and that this is what you needed to know.