I'm afraid I would have to disagree with that advice. Clean the magazine regularly by all means, but I wouldn't recommend steel wool and a screwdriver. The steel wool will “key” the surface finish of the metal, allowing dirt to stick and build up more easily - not to mention the likelihood of gouging the surface with the screwdriver.
I would suggest using kitchen paper wrapped around the shaft of a toothbrush. To clean a staggered-row magazine in this way, you can wrap a few layers of paper around the shaft, but with the single-row PPS magazine you'll only be able to wrap one layer around the shaft - which will then poke through the paper when you're in half-way. You can then simply withdraw and repeat from the other side of the magazine. If the mag is not too dirty, you can do without the toothbrush and simply draw the kitchen paper through.
The toothbrush shaft allows you to apply a bit more “elbow grease” when rubbing with the paper. I use the same method when cleaning the mag-well.
Balor