If a toilet has been working fine but suddenly flushes or drains very slowly, the problem is usually a clogged drain.
If you've plunged and snaked out the drain but your toilet still flushes poorly, it may be the toilet's siphoning action. When a toilet is flushed, water rushes from the tank, through the valve seat, around the rim, and through a siphon jet chamber built into the porcelain at the front of the bowl.As the water encircles the rim, some washes down through the rinse holes in the underside of the rim. The rush of water causes a cleansing action and creates enough force to push waste out through the back of the bowl and down into the waste pipe.
First open the tank and check the water level. A low water level means there may not be enough force to kick off the siphoning action. Toilets are designed so that the tank, when filled to the top of the overflow tube, holds enough water for a good flush. Water-saving devices such as dams, bottles, or bending the float rod will foil the design. You're better off getting a toilet that's designed to be a water-saving fixture. Flush the toilet and make sure the flapper allows all of the tank's water to complete the flush.
If the water level looks fine, the rinse holes may be clogged with mineral deposits, particularly where hard water is a problem. You can clear the rinse holes located just under the rim or near the back of the bowl, using a short piece of coat hanger (turn off the toilet's shut off valve and flush the toilet to get rid of most of the bowl's water, first). Lime remover can dissolve minerals built-up in the toilet's channels, but this will take 8 hours or more. The idea is to dam-up the orifices so the lime remover can go to work--pack the holes with wet paper towels and hold them in place with a generous supply of plumber's putty, then pour a bottle of lime remover into the overflow tube and let it sit.
An inadequate flush can be caused by a broken link between the handle and trip lever or a tank stopper that closes before the tank empties.
