It has been referred to as the john, the throne, the loo, the water closet. Call it what you want, your toilet may be flushing away oodles of water.

If you are like most people, the toilet accounts for about 30 percent of your home water use. Consequently, toilet manufacturers have spent the last couple of decades developing increasingly water-efficient models that combine form with function.

In the early 80s, the U.S. Government required all toilets manufactured to use a maximum of 3.5 gallons per flush. Although the new "water-saver" toilets used about half the previous amount of water per flush, poor engineering—and conflicts with existing drain, waste and vent systems—often required the toilet to be flushed a second or sometimes third time to fully clear the bowl.

What seemed like a good idea had in many ways backfired. The significant savings in water was not realized and many consumers were outraged at the need to flush more than once.

In an effort to save more water and reverse multi-flush syndrome, in 1992 the government again stepped in and said toilets must not exceed 1.6 gallons per flush. These newly engineered "ultra low flow" toilets use less than half the water of their previous water-saving counterparts and, on the whole, produce a more efficient flush by moving the water faster.

Since the toilet works in harmony with the vent and waste system, even the slightest abnormality can prevent the toilet from flushing properly. The root to some of the more common toilet flush problems can be linked to one or more of the following: a clogged waste line; a clogged vent line; a faulty flush assembly or clogged siphon jets the holes beneath the toilet rim.

So it's worth noting that the notion that a new toilet will solve your flush problems may leave you disappointed. That being said, all else being equal, a new toilet can save lots of water, conserve this natural resource and improve the comfort and appearance of your bathroom.

Since toilet shopping can be a daunting task, here's a guide to the three basic types of toilet flush operation:

--As the name implies, gravity flush uses nothing more than gravity to transfer the water from the tank into the bowl to create the siphon action. In general, a gravity toilet is the least complex, the easiest to repair and the most reasonably priced.

--A pressure assist toilet contains a pressurized tank that captures air as the tank fills with water. Although the early models of this style of toilet were compared to toilets found in airplane lavatories due to the "whishing" sound they made when flushed, they have become less obnoxious.

--The vacuum assist toilet is the newest toilet flush technology. The system allows the toilet to give a complete, clean flush using only the rim holes inside the upper toilet bowl. When a vacuum assisted toilet is flushed, a vacuum is created which draws the water with more force into the bowl. There is no siphon-jet hole in this toilet. With all the water that is coming out of the rim holes, the bowl stays cleaner.