One of the biggest pet peeves plumbers have is that people seem to think that Drano and Liquid Plumr are the solutions for any drain clog in the house. While these can be useful tools in some instances, in others, they can cause more damage than they are worth.
Why Shouldn’t I Use Drano in My Toilet Bowl?

Toilets are a special case, as any chemical you put in the toilet is going to stay there for some time, since the bowl fills with water and is slow to drain without flushing. The chemicals will settle onto the porcelain. Plumbers will tell you this is a bad thing because the chemicals in Liquid Plumr and Drano will heat up while standing in the ceramic bowl. This will cause one of two things to happen. First, it can crack the porcelain bowl, meaning you will have to replace the entire commode. Second, the concoction could explode, leading to replacement of fixtures, furniture, and perhaps walls in your bathroom. Both are much more expensive than calling a plumber to bring a drain snake for repairs or using a plunger.
Why Shouldn’t I Use Liquid Plumr in Other Parts of My Home?

There is no rule that says over the counter drain clog removers aren’t safe in some instances. For example, you could potentially clear out a really bad clog in your shower drain with one of these liquid agents. However, plumbers will warn you that, if you have plastic piping in your plumbing system, the chemicals in these agents will eat away at your pipes quickly. In fact, they can even begin to eat and corrode metal piping over the long term. If you use them too frequently or if the chemical doesn’t resolve the clog then it just sits in your pipes eating them away. For reoccurring clogs, you should always call for professional help rather than risk the cost of repiping your home.
Signs You Might Be Getting Played

Of course, if plumbers insist that you never use chemicals for small projects, they are likely just trying to make an extra buck or two. In many cases, a single use of Liquid Plumr or Drano isn’t going to cause an issue with your pipes, though you may still want to avoid use of harsh chemicals in the toilet. Don’t be guilted or frightened into getting professional help when it’s not necessary, but also know when to make that phone call to the trained and licensed plumbing contractor!