I am not a pet owner – so I never thought about the challenges involved in letting Fifi or Mr. Bigglesworth relieve themselves during a trip.
Apparently, the Washington D.C. airports did consider these challenges, because they just opened several designated pet relief areas.
At Dulles, two of these areas are actually inside the airport. Each of these fenced in areas has a fake fire hydrant, artificial grass and bag dispensers. To keep things clean, these locations also have special ventilation and a flushing system. Three other locations at Dulles are pre-secruity, outside the main terminal building.
At Reagan National, all the relief areas are outside the terminal buildings. They are located at Terminal A, B and C. A map of the locations can be found here. The relief areas were originally intended for service animals, but traveling pets are also welcome.