I read about Model 3s losing their bumpers due to filling up with water. When I look underneath at the rear diffuser and I see that there are some small holes where it meets the undertray for drainage, so I decided to make some enlarged holes along the slope. Drilling holes in cars always reminds me of this clip from the Simpsons.
I decided to perform this modification without having to remove the diffuser from the rear bumper as that was way too much work. This is where my "speed" holes are position and they do not interfere with the rear deep trunk section.