Dig the hole for the tank. Dig the center deeper. The weight of the water will bow the middle of
the rubermaid tank's bottom, making sloped center. There is no need to pretreat it with a heat
gun.

Don't tilt the tank. It's weird that way.

Lisa wrote:

Yes - that's how it will be. Bottom drain enters bottom area, water
leaves settle/vortex from the top. In the middle of the tank.

Just looking for ways to drain it easy. Wish I could heat gun it a
bit to dip down in the center, but I don't have the know-how or tools.
So I'll probably just tilt the tank to one corner.