Depends on what I am blocking. Now, keep in mind that this is what valves are for, but if the valve is wonky and you need to temporarily block water flow to fix, it could work. With my skimmer, I removed skimmer basket, put several large beach pebbles (too large to fit through hose) into a plastic bag, and put in skimmer. The weight of the water on top of the bag of pebbles made a seal.
For my return, I knotted a plastic bag and jammed it into the eyeball. It expanded and while I still had some water trickling, it didn’t keep me from working on the connection.
For my return, I knotted a plastic bag and jammed it into the eyeball. It expanded and while I still had some water trickling, it didn’t keep me from working on the connection.