|MadSci Network: Engineering|
Hi Mary, Actually it's for a couple of reasons. The first is that on most ships the toilets (heads) and the rest of the "black" water system are tied into the same salt water system as the fire hoses (for the incoming water). Because of this, they're under higher pressure than what you are probably used to. Secondly, due to the fact that ships aren't a steady platform (they pitch and roll with the waves), the septic system has kind of a vacumn acting on it that sucks the water out of the toilets. Depending on the ship, this may be a natural effect, or it might be a mechanical system. Hope this answered your question. John Metcalfe 3rd Mate Oceans (Unlimited) US Merchant Marine
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