Sulfuric acid, lye and sodium hydroxide are popular ingredients for opening a blocked drain. However, continued use of these poisonous and corrosive products can do more harm than good. Sure, they eat up whatever is in their way; hair, grease, dirt, etc. but also good bacteria and PVC pipes.
Good old white vinegar and baking soda can give you the same results and save you from breathing in dangerous fumes, hiding harmful chemicals from small children and animals, and helping to protect the environment. Every time we introduce chemicals into the atmosphere, through air, land or water, we decrease the value of a healthy environment.
When you first notice a slowing of the drain flow, pour ½ cup baking soda down the drain. Follow with ½ cup white vinegar. Allow the natural chemicals to work in removing dirt and debris from the pipes (about 15 minutes) and flush with boiling water. The baking soda will be made more alkaline by the boiling water making it more powerful against clogs. If the clog is of the more stubborn kind, heat the vinegar first before pouring it into the drain pipe.
You may find the use of a plunger helpful in pulling away the crud and sending on down the pipes. Use intermittently with the vinegar and baking soda procedure if more than one application is needed.
Vinegar and baking soda form carbon dioxide that literally explodes into a reaction of air bubbles and helps to scrub the sides of the pipe with the vinegar (acetic acid). Do not become alarmed if bubbles appear at the top of the drain. This is a natural reaction and harmless.
Once your drain is open (and smelling fresher), begin a maintenance program of pouring about 1 gallon of boiling water down the drain on a weekly basis.