The toilet doesn’t flush or is flushing slowly? The possible causes are numerous, many of which can be solved without the help of a plumber. You must start by inspecting the toilet cistern, as this may be the simplest source of the problem otherwise it may be necessary to clean the edge of the toilet with household products. If there are large scale deposits, it is sometimes essential to use muriatic acid (hydrochloric acid) or a drain cleaner.
Inspect the toilet bowl
Find the source of the problem. The term Toilet doesn’t Flush can mean two phenomena: the toilet bowl does not fill quickly when you flush it or the toilet does not quickly eliminate waste products. In this second case there may be an obstruction and you need to remove it; if, on the other hand, the problem concerns the toilet, you just have to check the tank.
Lift the lid of the cassette.
This is the upper and vertical portion of the toilet, to which the button or handle that activates the drain is connected. Gently rest the lid on the ground, it is sometimes made of heavy ceramic and may damage the tiles.
Check the chain that connects the drain knob to the cap. The latter is a piece of rubber or plastic that is located above the valve, at the bottom of the box; unless the toilet is draining the water at all, there should be a chain connecting this element to the flush button / lever. 
The chain should have enough slack to allow the plug to rest on the valve and close it; however, it should also be tight enough to turn it up promptly when you flush the toilet.
Adjust the chain if necessary.
This action is quite simple, the chain should be inserted into a hole in the knob; you can easily disconnect it and use another link to connect it to the flush control, thus changing its length. Remember that this element should have about 1 cm of clearance. 
As you proceed with maintenance, you come into contact with the water contained in the tank; as long as you wash your hands after the job is done, this is completely safe.
Use Dish Soap and Drain Cleaner
Pour 4 liters of very hot water into the toilet using a bucket. Almost boiling water helps loosen debris that could slow down the drain. Do not flush the toilet but let the water stay in the toilet bowl.
Pour the toilet cleaner into the toilet. Make sure you are using a specific toilet product;  you should find detailed instructions for use on the package that also cover dosage.
Read the label carefully, as some substances must not come into contact with the ceramic and it may be necessary to use protective equipment. Always respect the directions you find on the package; in some cases the toilet must be flushed immediately, in others the product must be given time to act.
Pour the dish soap into the overflow tube.
The latter is located in the flush tank, in a vertical position, and is generally equipped with another small tube that is inserted into it; you should pour a small amount of soap into it, about a tablespoon.
Wait ten minutes.
In this way the soap can penetrate into the overflow pipe; meanwhile, the cleaner removes calcium and other deposits from the toilet walls simplifying the cleaning process.
Flush the toilet.
This procedure allows you to send the water through the pipes of the tank and out of the holes that are located under the rim of the ceramic cup. The dish soap should loosen any residue, while the drain cleaner should loosen any blockages or lime scale deposits, improving toilet flow
Take the necessary security measures. Wear gloves, a mask and goggles; you should also put on an apron and rubber boots. Make sure to maximize air circulation in the room by placing a fan on the bathroom window to suck harmful gases outside; if the room has a vacuum fan, turn it on