Chemicals
Portable Toilets use a smell reducing chemical (deodorizer) in the holding tank. This chemical is typically blue so that when it interacts with enough urine & feces it turns green. This green color is an indication that the chemicals are no longer effective in preventing odors.
In most states a formaldehyde (embalming fluid) based chemical is used to neutralize odors, this method of deodorizing the portable toilet has proven very effective. The formaldehyde based chemical interferes with the bacteria in portable toilets, these bacteria release odorous gas when breaking down waste. A notable exception to the formaldehyde based formula is California who has banned the use of this chemical in portable toilets, RV's and the like because it interferes with their sewage plant operations. A much more environmentally friendly enzyme is used to break down the waste while releasing a fragrance. This enzyme does not prevent the bacteria from breaking down waste but actually helps break down waste itself. Because it doesn't directly deal with the cause of foul portable toilet odors its much less effective than the traditional formaldehyde based solution.
A much older form of portable toilet chemical is Lye. Lye was used during the old "wooden outhouse days" to prevent odors. After a person is done using the portable toilet they would grab a bit of lye and sprinkle it into the holding tank.
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