Early Sept. (25th thru the 1st) is it still very hot and humidor is the weather becoming more tolerable by the end of August?

hot, humid, unless you are really lucky.

August in DC is just as bad, or worse, than June and July. In fact, our weather in the mid-Atlantic and southern states all along the eastern seaboard are consistently experiencing "summer" temperatures through September and even into October.

That phenomena used to be intermittent, and was given a special name: Indian summer. It is now a given, and is just . . . the weather.

Could that mean anything?

To answer the OP, I'll say yes to both her questions-- the weather usually seems a bit better by the end of August but it can still be hot and humid, just less so than in late July. I think the worst of Washington summer weather is usually from late June to mid-August.

The advantages of visiting Washington in the week before Labor Day are greatly diminished crowds, and rock-bottom hotel prices (and maybe somewhat better weather than earlier). Congress is in recess, there's almost no convention business then, and family travel drops as schools reopen. A few restaurants close that week, but not many.

Yup, hot and humid. Probably more tolerable than July. Avg August temp is 87 degrees, vs July's 89.