Having a toilet that doesn't flush all the way can be a real pain. Not only is it an inconvenience, but it also makes it more difficult to keep your toilet clean. Having to flush the toilet multiple times will end up wasting a significant amount of water as well. It might be that one of the internal components is damaged and in need of repair. To find out what might be causing your toilet to have problems flushing, check out a few of the parts below.
Take the lid off the back of your toilet tank. If there is a lift chain in there, you want to take a look at it and make sure there isn't a bunch of slack in it. If there is too much slack, the flapper isn't going to be able to raise up as far as it should. This prevents the toilet from getting the water it needs to flush all the way. To get the flapper where it needs to be, you can simply adjust the chain by taking it off the flapper and reattaching it to one of the closer holes. It might take you a few times to get the length just right, so be patient.
This tiny piece of rubber is what sits on the bottom of your toilet tank and lets water come into and out of your toilet tank. As you flush your toilet, it raises up and allows the water to go out of the tank and into your toilet bowl. It then goes back down and covers the hole to let the water fill back up again for your next flush.
Flappers that are damaged, warped or worn won't be able to sit on the bottom of the tank properly. When they aren't able to seal off the hole, it allows the water to continuously leak from the tank. Because of this, your toilet isn't going to be able to flush properly. To replace the flapper, you will need to turn the water off to your tank. Flush the toilet to get all of the existing water out. Then, take the old part off and put the new one on. Turn your water back on and you are good to go.
While these are only a couple of parts that could be bad, there are others as well. If you ever have any questions or concerns, you can always discuss them with a local plumber.