I installed a paver patio and had a couple of downspouts I needed to route across the patio, didn't want to trip over them, but didn't have the slope to reasonably bury the downspouts - so I found "Paver Drain" from Stegmeier which fit in nicely. These printed adapters adapt my 2x3 metal downspouts into the end of the paver drain which then slopes to the outside of the patio. Works well and looks nicer than any of the other alternatives that I found.

Printed in whatever PLA I had around and then painted with exterior paint. Have lasted 6 months and seem fine, but if they show real issues will consider re-printing in PETG.