Originally Posted by
boatnfish
I would walk into any of the major hotels like I knew what I was doing and ask to check my bag for the day. Act like you were staying there and just checked out but not flying until later in the day.
this is good advice. The luggage storage in Union Station is a bit expensive. (If I recall, it is by the hour and general size of the bag. My bill for 2 bags for over 4 hours was almost $40). There are plenty of hotels near Union Station (Hyatt, Washington Court, etc) where a good tip would still be much less and still in the same basic location.
Still, if you want to use the luggage storage in Union Station, it is near the departure area for the Amtrak lines. If you are facing all of the Amtrak gates, head to your left till you reach the end of the gates, it directly across from a restroom.