I experience the air conditioning in my house every day in Texas this time of year. That doesn't make me an expert on how the AC actually works.

Let's call you what you are - a "veteran passenger". That does not make you an expert on how aircraft mechanically operate because if it did, you might have actually been aware of the fact that the lavs have two different systems for flushing - one that operates the lav on the ground and below 16,000 feet and one that operates the lav above 16,000 feet.