Remove echo when recording in say, a hallway Sorry if this is the wrong site to ask this question, with it not being strictly about video.

Say I’m conducting an interview in a hallway or similar environment. There are a lot of flat surfaces, maybe an uncarpeted floor, this is going to produce a lot of echo and sound distortion. A purpose-made room or studio isn’t an option as the interviews are supposed to be “of the moment”. How would I go about eliminating echo?

I can’t go around the whole location putting up blankets to dampen the echo, so would I be looking at some sort of attachment on the camera microphone, i.e. a windsock (or similar attachment if a windsock isn’t appropriate)?
The attachment you are looking for is called a lav mic, though sometimes it can be a hand-held shotgun mic, too.  Sound intensity decreases as the square of distance and echoes decay exponentially.  The trick to eliminating the echo is to get the mic sufficiently close to your sound source that the original source is 10dB to 20dB louder than the environmental echo.  If you see how close a news reporter holds a mic up to a subject when interviewing them in the moment (and sometimes in a hallway), do that.

There's nothing you can put on the microphone that will solve the echo problem.  The only way to solve it is with proper distance (which is a function of proper distance ratios).