This is what I do. I'm sure some will disagree with it but this is what I do and have had zero issues. I rinse out the keg, then fill it with a gallon or so of hot water and pbw. Shake it around a bit. Then I let it sit for a few minutes, while its sitting I remove the liquid post and lid and set them in some hot water and pbw. After the few minutes I drain the keg and rinse with hot and cold water again. Also rinsing the lid and post, and then I fill it with some cold water and star-san and shake it around a bit. Before I put the post back on I spray it down inside and out with my star-san mix I keep in a spray bottle. I have had zero issues.
I agree with the cleaning method but I use about 1.5 to 2 gallons of water pbw mix. I lay it down with everything connected still and quarter turn it every 30 mins or so. This way I can cover the entire keg and better yet if your during the process of cleaning equipment I use the mixture to clean out my equipment as well, no sense in wasting PBW.