This plugs the end of a 3 Inch PVC pipe.  Perfect for blocking the ends of kayak trailer bunks that use 3" PVC pipe.  I drilled a small drain hole in the bottom of the back plug after it was installed so that water that got into the bunk from the installation holes could find a way out.

Use a filament that can handle outdoors such as ABS, ASA, or PETG.  This is a snug fit but not friction fit, it will need an adhesive to stay in place.  I used a 5 minute epoxy.  Printed with 3 walls and 45% infill.  I printed mine with the outer surface down and with supports.  You can also print them with the inside down and use supports for a cleaner exterior look.  Since mine is going on a kayak trailer, I didn't really care what the outside surface looked like.