Here is a list of some reasons wastes are not cleared from a bowl when it's flushed the first time.....
Some of this information is repeated on other pages, but because I'm getting so many e-mails about "lazy" toilets, I'm addressing it here as a separate topic. The Lazy Flush is a builtin problem with some of the newer 1.6 gallon toilets. You'll find a lengthy discussion of the 1.6 gallon toilets under Low Flow Toilets with some suggestions for solutions.
Water does not enter the bowl fast enough.
Remove the tank cover and observe the action of the flush valve as you turn the handle. When you let go of the handle, does the valve stay open long enough for most all of the water to leave the tank?
If the flush ball or flapper is closing too fast, replace the ball or flapper, then make sure the chain in just long enough for the ball or flapper to close, if it is too long the valve won't open far enough and stay open long enough to allow all the water to leave the tank.
Clogged Rim and Jet Holes
Foreign objects can get into the rim of the bowl or jet channel to clog them. Use a small hand mirror to examine the rim holes as you flush the toilet to see how much water can enter the bowl through the holes. The holes can get clogged with mineral deposits from the water. The rim can also get clogged with something from the inside the tank that has gotten into the rim channel. I have heard of such things as the labels from the toilet tank deodorizer bottles clogging the holes and gauze from bandages; it's anyone's guess why gauze would be in a tank. Although, I've been told nursing homes have a problem with some residents "hiding" all sorts of things in the toilet tanks.
If you find grayish mineral deposits, sometimes you can dissolve them. Begin by first removing as much water as possible from the bowl by dumping a bucket of cold water into the bowl all at one time. This will leave you with a small amount of water in the bottom of the bowl that you will have to sponge up. Next, thoroughly drying the bowl and rim, then cover the jet hole in the bottom of the bowl and all the rim holes with a heavy duct tape. Finally pour white vinegar into the overflow pipe in the tank. The longer the white vinegar remains in the channels, the better chance it will have to soften the minerals.
Test the jet hole by putting your hand in front of the jet hole in the bottom of the toilet bowl and see if a strong stream of water is entering the bowl as you flush the toilet. A plumber once told me he had extracted a rubber washer from the jet hole (someone had probably dropped it in the tank while doing a repair, and it washed into the rim and then into the jet channel).
After the minerals are softened, use a small pick to ream out the holes. If on the other hand, you think there is something such as labels in the channel, you'll just have to use tweezers to clean out the holes.
Unfortunately, there is a water saving idea that has circulated for years, that says if you put a brick in the toilet tank you use less water per flush. It's a bad idea and shouldn't be used, because the bricks can disintegrate and crumbs will wash into the bowl channel and clog the holes. If the channel becomes clogged with brick crumbs, you are probably going to have to replace the toilet bowl. You can achieve better results using a plastic milk jug filled with enough marbles or gravel to keep it from floating.
In addition, a brick will not displace enough water to matter. There is always an inch or so of water left in the tank when the flapper closes and the tank begins to refill. Bricks are heavy; you could crack a tank if you accidently drop the brick inside the tank.
Tom in PA has this to add: "Your advice on diagnosing & fixing "lazy flush" was right on! I was 12 hrs. away from buying a new toilet. I found chunks of "chlorine tablets" about the size of a $0.50 piece in the vent holes under the front rim. They obviously dissolved enough to make their way from the tank but not into the bowl. Please pass on the hint. Thanks again! "
Plumbing Parts and Products