When you have a clogged drain and cleaning the trap doesn't work, do you reach for a caustic cleaner? How about trying a very simple alternative.
I use 1/2 cup of baking soda, pour it down the drain, followed by 1 cup of white vinegar. It will fizz upon contact. You want to keep the fizzing in the drain, so cover it if needed. Let it sit for 10 minutes then pour 1/2 - 1 gallon of boiling water down the drain. This should release the clog. It can be treated a second time if needed.
To clean a smaller drain, such as that in a bathroom sink, I use half of the recipe.
It works great and the best thing is, you've probably got those items already on hand!