Toilet flapper, one-piece vs. two-piece toilets, black substance

QUESTION: Three years ago I purchased a Kohler low-profile toilet. I have had to replace the flapper three times. Also, the handle never returns to the “off” position regardless of how many times it is adjusted. Currently, there is a black substance appearing in the bowl, not in the tank. What is going on?
Beverly Fitzpatrick, Orangevale
ANSWER: “By low-profile toilet, I assume you mean a one-piece toilet,” says Vince McDonald, owner of McDonald Plumbing, Heating & Air Conditioning in Sacramento.
“One piece toilets look nice and are normally quieter than a traditional two-piece toilet, but they are more complicated to work on. Most toilets’ flushing action is accomplished by gravity. The whole tank of water sits above the toilet bowl and when the tank is flushed, gravity sends the water out of the tank and into the bowl. It is a simple, reliable system.”
“However, because the water tank of one-piece toilets is not entirely above the bowl, they would do a very poor job of clearing the toilet bowl with a gravity flush alone. So manufacturers have designed them to use the power of the tank fill water to assist the flushing process. Some models, called pressure flush or power-assist toilets also use a pressure tank to aid in the flush.”
“It is unusual to have to change the flapper so often. Perhaps you are using a part that is not of the same quality or exact design of the factory original. Make sure you use only factory parts. The black substance in the toilet bowl is probably mold or mildew growing in a constant flow of water into the bowl because the flapper is not holding back the water in the tank. When you stop the constant water flow, the black mold should disappear. The handle never returns to the ‘off’ position because the rotor – the part that diverts the water into the bowl when the toilet is flushed to aid in the flushing process – is not properly adjusted or is worn out.”
“If you continue to have problems with the toilet, call a plumbing professional who is familiar with your toilet. A constant flow of water through your toilet can damage the toilet as well as the seal at the floor, so it is a good idea to get it repaired soon.”

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