What is happening and how do I fix it?
Signed, Clueless in Seattle

 

firecrackerjuli, Welcome to the DIY Forums.
Lets discuss how a toilet works. A toilet has a built-in trap. Just like the ones under your sinks. A "U" shape that holds enough water to seal out sewer gases. When the toilet is flushed, it takes all the water and whatever else is in the bowl and pushes it through the trap and when the trap is full again, all excess water goes down the drain.
There are a couple things that may be happening to you.
1) The holes in the rim (underneath) are partially clogged and not allowing enough water to flow at one time to complete the flush. Cure: Turn off the water supply under the toilet. Flush the toilet. Lift up the flapper in the tank and pour a bottle of vinegar into the hole where the flapper is. Let this sit for as long as you can. Take a mirror and a bent metal coat hanger and push through eack hole under the rim. Turn the water back on and flush.
2) The flapper is not staying open long enough to allow the tank to totally empty. Cure: Adjust the chain from the handle to the flapper so that the flapper "just" seals. This way, when you activate the handle the flapper will stay open longer.
3) If the water level raises when you flush, there may be a clog or partial clog in the toilet piping. This will have to be snaked out or PERHAPS an enzyme drain cleaner used to "eat" the clog.
Good luck and let us know how this works out. You can do these in any order you wish.