Very simple version of a pipe cap, can be customized for size. It's meant to be printed so the "hold" section is a bit larger than the pipe you mean to cap, so you can wedge it in there. It's not going to give the strongest hold, but it's only meant as a dust/rain cap.

I made this for an old gutter pipe that was connected to the city sewers at my house. They incentivized disconnecting gutters from the sewers some years back, but the drain pipes remain. One of my caps was missing, and this was a quick fix.