My greenhouse is located on a nine degree slope, Watering is always a challenge since with a normal watering can the moisture always puddled up and ran downhill, I purchased an expensive British made watering can with an very fine rose and the fine spray delivered solved the problem. I am growing winter crops with no external heat and note this fine rose is plugged up and I would like to clean it properly. Simply trying to flush water through the rose under pressure does not solve the problem and is messy. Is brass cleaner the solution?
Proper cleaning will depend on what it is that's clogging up the nozzle. My guess would be mineral deposits/hard water in which case something like vinegar ought to work (may need to let it soak). Not sure if vinegar will be good for brass or not so you might want to search a bit to see if you can find more info before you try it. Brass cleaner certainly won't hurt anything and on the chance that it's slightly acidic it may help so you might try that first but typically metal cleaners like that are designed mainly to clean up tarnish on the metal so I don't know that they'd do much for hard water. Or if you'd rather do something mechanical rather than chemical, if you have a needle or piece of fine but stiff wire that fits inside the holes of the rose you could try that to clear them. Might take a long time though because I expect there are a lot of holes!
I suspect that any acid will discolor the brass. If you want to do it mechanically you can always buy a set of tip cleaners from a welding supply house, TSC,Harbor freight or some hardware stores. They are a series of small stiff wires of graduated size that have a file like surface. They are designed to clean the ends of torch tips. The last set I bought was $2 although I wouldn't be surprised that they are $5 now.