Washington Capitals
627 North Glebe Road
Suite 850
Arlington, VA 22203
Put an 'ATTN:" line after the address to direct the letter to the proper party (IE, player name, community relations, youth...
Without a payment:
Department of the Treasury Internal Revenue Service Ogden, UT 84201-0005
With a payment:
Internal Revenue Service P.O. Box 105083 Atlanta, GA 30348-5083