When it comes to that little cabin behind the cabin, better known as the aircraft lavatory, the average passenger cares far more about whether it works than how it works.

How important is reliability? Important enough that in promoting its new Model 650 business jet, Savannah, Ga.-based Gulfstream makes a point of assuring that its toilet "always flushes" (or more precisely, will always flush, since the new jet won't make its first flight until 2009). After all, lavatory amenities such as granite countertops, rosewood veneers and brass trim are quickly forgotten if the toilet doesn't work.

That said, not all working toilets are created equal. You'll find three basic types on business aircraft, and they differ in significant ways. The earliest type-which, thankfully, is now rare-features a simple basin fastened under the seat (the classic "honey bucket"), to be emptied by hand at the end of the flight. This undoubtedly is not high on the list of favorite jobs in the aviation industry.

A second toilet system, typically incorporated in small to midsized business jets, is known as "recirculating blue water." This system employs colored water (due to sanitizing and deodorizing agents) that is filtered and recirculated to save weight. It costs about $15,000 plus installation.

The typical complaint by passengers in aircraft with a recirculating blue water toilet is odor, particularly on long flights. Also, the system is usually serviced through the cabin, which is less than ideal, since the possibility of spillage exists. Some of these systems, however, can be installed with a package that allows for service from outside the airplane.

A third type of toilet uses a vacuum-flush system that deposits waste in a sealed chamber. The system is effective, but its size makes it suited only for large business jets, such as Bombardier's Global series and the Gulfstreams. And while prices for the toilets themselves start at a relatively reasonable $25,000 plus installation, they require a system to allow external servicing that costs about $175,000.

The vacuum-flush system, incidentally, uses the same blue water as a recirculating toilet, but much less of it. And Monogram Systems of Carson, Calif., recently announced a patented innovation that can reduce a vacuum-flush toilet's water use even further-by up to 50 percent, the company claims.

Technology flushes on.

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One less thing to worry about

Some people have a fear of flying; others apparently worry about getting stuck on the seat of a vacuum-flush aircraft toilet. Despite the loud noise accompanying the flush, however, the duration is less than three seconds and getting a sufficient "posterial" seal in that time is impossible.

In fact, television's MythBusters took on the task of examining this concern and reached the following conclusion: "With a properly functioning, modern airplane toilet, it's not possible to become stuck to the seat in the manner described, and even if it did somehow happen, the suction would be so weak that unsticking yourself wouldn't be any tougher than standing up normally."