Many times it is possible to unclog a toilet by pouring dish washing soap and very hot water into the toilet. The soap provides lubrication to move the clog through the fixture. A large pot of water increases the pressure and mixes with the soap to dissolve fats and allow the clog to move forward.
Toilets operate using a siphon. The waste exits through a small opening in the bottom of the bowl and travels through a trap into a larger pipe. Most clogs take place in the trap, which is a part of the porcelain of the toilet. Moving enough of the clog to allow a small amount of the water in the bowl to flow through the trap allows the water to erode the clog and open the drain.
Many commercial drain cleaners are safety hazards. They contain toxic and corrosive chemicals that cause burns or damage the eyes. Mixing these chemicals also has the potential to cause violent chemical reactions. If pouring soap and hot water down the toilet does not free the clog within 30 minutes, a better option than using these dangerous chemicals is using a plunger or closet auger to remove the clog through mechanical means. If the clog remains after use of these tools, it is time to call a plumber.