Sightseeing ideas & luggage storage near Union Station/National Mall in Washington DC
 

Hi. Are there public luggage storage/locker facilities near Union Station or on the National Mall in Washington, DC? I've searched online but encountered lots of out-dated info. I already contacted Union Station and was told there is no luggage storage facility there or nearby. I'll fly into DCA early morning on a Monday and leave for NYC by bus late afternoon same day. I want to do a bit of sightseeing, museums and galleries and perhaps do a photography walking tour on the National Mall for about 6-7 hours without luggage in tow. Already, I snatched up one of those free tickets for Guided Tours of the US Capitol. What are some must-sees or must-dos for the short amount of time there on a Monday?

I'll have with me one checked bag, a roller carry-on and a backpack. I do not have lodging and will take public transport only (DC Circulator bus). Any pointers or recommendations about luggage storage solutions or cheap sightseeing would be appreciated!