If you have 3" PVC drain pipes that have drain adapters and covers, these are a couple replacement covers I created. The diameter of the part that slides into the drain pipe is 3.25", its length is 1.5" and fits nicely in standard PVC pipes drain adapters. One has a lip on the top to give it more strength and support by resting on the top of the pipe. The other is identical except it has no lip and can slide in flush to the top of the pipe. Aside from additional strength, the lip provides a nicer finished look IMHO. Choose whichever you prefer. While the commercial ones aren't too expensive, the best thing for me is I can pick whatever color I want. My deck is dark brown stone so bright white drain covers are a bit of an eyesore. Now you can just pick your matching PLA color and get a cleaner look.

I've also made the "blades" of the drain grill a bit wider and deeper than what you get from Amazon for extra strength. I find the ones from Amazon break out the drain blades pretty easily after a bit of use. These should take more abuse.

I printed in white PLA for my test prints at 30% infill and 3 exterior walls and the results seem quite strong,. We'll see how they hold up over time in the sun and rain. You can always use ABS or some tougher material. Remember, people will be stepping on these so make sure you make yours sturdy. You can print as coarse as you like as the model doesn't seem to suffer from it and you get faster results.

Print the model grill down and there's no need for supports or adhesion being on. It should just load into your slicer (I use Cura) in the correct orientation for printing.