Non-permanent way to cap a clay cleanout pipe
A big stone is very good. Or, a 12x12 or small concrete paver from the store will also work great. Or, you may find smaller metal (you need UV proof) trash can lids at the store. A rock can go on top of the lid or a rock can be attached or hung from the lid inside the pipe. Or, you can get some concrete or cement mix &amp; make your own custom cap.