Using a hole saw for the initial cut is a good call, and pointing folks to the example pics really helps them visualize the setup before they start.Hobbs: It was a hole saw. As for the scrubber, check the examples link below, and find the pics; they will tell you the site. Then just search for the username on that site.
Dawn: Mesh does not really matter, although I use 7. For pipe, from the pump to the scrubber, 1 inch is fine. For the scrubber drain, bigger is better. You do not need standing water in the scrubber box.
And you’re right about the scrubber — mesh size is flexible, and 1‑inch pipe from the pump to the scrubber is plenty, while a larger drain helps avoid any standing water issues in the box. Good practical advice!