The Mailboomer in DCA is not Fastpass, but does have a single rider line. We had extremely short waits in the Maliboomer single rider line.
Keep this mind on Fastpass use: Your FP ticket will give you a one hour time frame -- For example: 10:00-11:00. Even though you have not used your FP, you can get a second FP once the first time has started. (In this situation you could a 2nd FP after 10:00, even though you have not used your first one.)