over time if you have hard water you will get a build up of calcium, this buildup does not allow water to flow as it should.either replace the entire toilet bowl, this should cost you no more than $80.00 a very easy job to do yourself. or try pouring not dish soap but CLR thats calcium lime,rust inhibitor. let it soak a long time and using your toilet brush to scrub all the inside of bowl; as possible.
TO REPLACE TOILET
turn off water flush toilet use wet/dry shop vac top syphon remainder of water unscrew water hoses remove toilet seat ( new one does not come with seat ) loossen and remove retaining bolts on floor remove toilet get the new toilet and apply plumbers wax around the seal place the new toilet on the floor bolts use the fasteners to secure toilet to the floor reconnect toilet water hoses and turn on water give it a few minutes to fill with water and try flushing if this solves your problem the reinstall tolit seat and cover onto new toilet
YOU HAVE JUST SAVED ABOUT $500.00