The toilets recently tested by Consumer Reports range in price from $100 to $425, and if you're not intimidated by a little plumbing work, you can install one yourself to save on a plumber. But as you're finishing, you might need to make one simple adjustment that, if ignored, can affect flush performance and raise your water bill.

As you can see in the tank for the $240 Gerber Avalanche HE-21-818, one gravity-fed toilet from our toilet tests, the toilet's fill valve has a screw that determines the height of the float—how high it rises before the fill valve cuts off incoming water. (The float can be external or mounted on the shaft of the fill valve.) Either way, when you've properly adjusted the screw (see photo), water filling the tank after a flush stops when it reaches the fill line marked on either the tank or the overflow tube.

"If the water level in the tank is too low, you won't get the powerful flushing you expect," said project leader John McAloon, who conducted our latest tests. "And if it's too high, you're using more water than the toilet needs to do its job." McAloon added that while the flow-rate adjustment screw should be set properly at the factory, it still needs checking during installation. Look in the manufacturer's instructions for specifics. Some toilets, for example, have another way besides the usual screw to make the same adjustment.

Want some more information on shopping for a toilet? Check out our buying advice, along with this video on our tough toilet tests.