It sounds to me like some sanitation related problem. We all experience the trub in the bottom of the keg. That is no big deal. Maybe the soap is affecting the taste if there is any residue. If it is a small beer just leave it in the primary up to thrree weeks or so and then rack to the keg. I usually give it another week or so to condition and then carbonate. Then the first pint or two gets rid of the trub and we're good to go.