Removing an Echo

I found a stereo video recording which was seriously disturbed by an echo -- bouncing mainly off a back wall. I tried three solutions with a sophisticated audio editor, all three of which were suggested on the Internet. But I could hardly tell the difference. I assumed this: that the main echo could be timed by the distance to the back wall. I therefore split the stereo track in two, shifted one channel by the "distance", inverted it, and reduced the amplitude. This made a significant difference to the recording. One could do yet more, if one identified other sources of echo and their amplitude.