I've been whiling away another boring lockdown day by watching one of the excellent Pilots Eye videos, this one following a crew in an Air Berlin (ah the memories) B737-800 from Munich to Hurghada. They were discussing pax moving about the cabin and the resulting effect on trim as they get up and down to use the lav, the joke being 'the worse the food, the more the trim'. Who says Germans don't have a sense of humour?
They also pointed to the cabin diff gauge on the overhead and showed the needle climbing up a little before returning to normal, saying that when the lav was flushed that cabin air was vented overboard. I didn't quite understand this, but this was with English subtitles of German dialogue so maybe something was lost in translation. I know that the 737 uses a vacuum lav, but how is that connected with the outflow valve? Is the air that gets sucked into the vacuum lav vented overboard? I've never heard of this one before, so was curious.
Thanks in advance. RU