PBW and Aluminum Kettle

Finally picked up some PBW since I've heard oxiclean is not good to use with aluminum. When I cleaned my kettle pre-brew yesterday, I had some weird white and shiny coating on the bottom of my kettle. I boiled a bit of water for a half hour and rinsed it out (white/shiny still there), said RDWHAHB, and brewed my new ipa.

My question is: now that I'm looking to clean the gunk off my aluminum kettle with PBW, what's the "right" way to do it? Should I boil an ounce or two of PBW in 5 gallons of water and let it sit overnight? Or is that bad for an aluminum kettle?

Also, can I use PBW on my auto-siphon? If not, what's a good cleanser for plastic/rubber?