USPS Priortity mail boxes reusable?

For what it is worth all mail classes get handled the same, except for Express mail. Retired from the PO a few years ago. Most mail gets, at least stuff going by air, transported by FedEx. The PO loads Pods that are flown by FedEx. Sure, this is probably not what you are going to hear from the window clerk, but it is the truth. http://www.usps.com/communications/news/press/2006/pr06_048.htm does not mention parcel post but trust me, it gets moved with first class/priority mail, space permitting...might want to read here also http://www.usps.com/strategicplanning/cs06/chp4_004.html , at least the first full paragraph.