Step 8: Inflate and Bubble Test
Fill a tub with water. Push the tube underwater and look for bubbles.
Once you find the leak, go look and feel around inside the tire until you find the nai/thorn/bullet hole or whatever caused it. Don't forget to fix the cause of the leak so you don't just get another leak.
These leaking bubbles are coming from around the valve stem. That's trouble. I don't have any patches with a built in valve. They exist but the nearby auto parts store doesn't carry them.
I think I remember what caused this leak originally. Various friends were riding this motorcycle to learn how to ride. They didn't notice that the rear tire was low on air. Jerking around with the clutch made the loose tire spin on the rim. The tube stretched and ripped a little here at the stem.
Alex, Alison and I cobbled a patch around the stem by cutting a hole in the middle of the patch. That held for a couple of years, but the stem rusted a little and that opened the leak again.