For reasons I can't get into because I don't know who might be reading, I need to completely flood Golarion. To get that much water, I'll need to import it from another plane, possibly using rifts. From what I understand, the largest planar rift was caused by killing a god, so currently I'm exploring that angle. I just need to hammer out the fine details, and I'm woefully undereducated about planar science.
First, how do you know which plane you're opening a hole toward before you kill said god? Is it a matter of astrology or do I need to just kill them all until I find the one I want? Is there another way I haven't considered yet?
My DM is actively encouraging this, but he's super busy writing the plot so I figured I would do the research solo and present the results when I have enough information. Anything you give could be useful. Thank you!