Lye, which is also known as sodium hydroxide or caustic soda, can be a powerful drain cleaner. It has a variety of cleaning and other uses, both in industry and in the home. If you will use a lye-based drain cleaner on your PVC drains and pipes, always ensure that you're using the proper concentration because lye is a corrosive substance and especially so at high concentrations.
PVC is an abbreviation that stands for polyvinyl chloride. Classified as a thermoplastic polymer, it's the third most widely manufactured plastic in the world. PVC is widely used in construction and home building because it's inexpensive, durable and fairly easy to assemble into complex piping systems. This versatile material is characterized by light weight and low reactivity, meaning it won't be easily affected by most chemicals that it contacts, including lye drain cleaners.
Chemically, lye is a highly caustic metallic alkaline base, meaning it has a pH of at least 7.0 or greater (all the way up past 14.0), making it the opposite of an acid, which has a pH of 7.0 and lower. Most lye drain cleaner solutions come in liquid or powdered form, depending on what they're mixed with. Powdered lye cleaners are usually combined with aluminum in varying amounts.
Because lye is so caustic, it can be extremely corrosive to certain types of metal as well as several other materials. Fortunately, though, PVC drains and pipes are characterized by their low reactivity, which means they can stand up well to this caustic and corrosive base substance. However, given a high enough concentration, PVC can be damaged just as much as any other pipe or drain material if you exceed recommended strength levels.
Lye is very effective at unclogging drains, and PVC drains and pipes should have no problem tolerating the chemical as long as it's used according to direction. However, you should always read the cleaner's label to ensure that what you're using won't damage your pipes regardless of the material they're made from. And never combine lye with other chemicals such as acid-based cleaners. Explosions and possible personal injury can occur if you do.