While working on the walkway, on one cold morning, I nudged the hose leading from the rain barrel, and broke off the little nozzle at the bottom of the rain barrel to which the hose was attached. This was unfortunate, since the whole rain barrel appears to have been made as one big solid piece.
I figured the best way to repair the rain barrel was to drill a hole where the nozzle had been and insert a new nozzle. I found something like this at Home Depot.
This is a barb on one end, suitable for slipping a hose over it, and 3/4 inch threads on the other end. So now I needed to drill and thread a 3/4 inch hole. Turns out I have a tool to create the 3/4 inch threads from my work with the PVC underground irrigation work:
This has 2 or 4 different threadings, one of which is just what I needed. So after drilling a smaller hole first, and then expanding it with the threading tool, I was able to get the adapter screwed into the rain barrel, and re-attach the hose.
An alternative, if we need one in the future, is to put in a brass adapter, but with a plastic rain barrel, a plastic adapter seems reasonable.