Harbor Freight, bro. Walmart of tools if you've got one in your area, and second only to a hydro shop for useful shit. I used a different method to cut super clean holes in my rubbermaid, but it might not work if you need an 8" hole. Take a soup can that has a diameter a little smaller than the net pot you want to use, eat the soup, cut off the lip of the can with a sharp blade tool. You should now have a can with a relatively sharp circular lip. Turn your range on high, set the can on top until it's hot as fuck, then pick it up with an oven mitt and press it down into your rubbermaid lid. Hot knife into butter. It smoked a bit when I did it, so ventilation is important, but it wasn't any worse than dropping a plastic spatula on the stove by accident.
You might be able to find a coffee can or something that will make a hole big enough for your needs.
