spannerhead, you are quite right in what you say regarding using a servicable bog to get rid af crap from a u/s one. On 767's, the usual suspect is the dreaded 'U' bends just aft of the mid bogs, and that is seats out, floor boards up, et al. Not a nice job, but worth a bob or two. If vinagre and ice were used daily, then it reduces the occurance of stuck bogs, but if course it costs, so the bean counters won't sanction it. And if you haden't guessed, I hate working on bog systems, Racasan or vacuum.