After taking down the sunroom (still a work in progress, which I’ll eventually post about), this pipe for a downspout was no longer needed. I temporarily covered it with a bucket to keep the critters out.
I needed a PVC cap to fit either the inside diameter of 4.5″ or the outside 5″. None of the local hardware stores carried the right size though; their inventory jumped from 4″ to 6″. I took a scrap piece of treated lumber and made my own cap.