We know what is required in France by the simple signs displayed at their pools but it seems that in DC the DPR gives out far more detail on the regulations:
http://www.popville.com/2013/07/dpr-...-for-dc-pools/
Your basketball shorts must be left at home but you can bring your long* swim briefs and your short swim briefs.
*what this contradiction in terms means is beyond my comprehension but the illustration of long appears to show jammers.