Commercial drain cleaners or openers are highly corrosive and dangerous to use.  This is because their main ingredients are sodium hydroxide (lye), a caustic that can burn the skin and cause blindness if it get into the eyes, and sulphuric acid, a corrosive chemical that can also cause severe skin burns and blindness.  Both types work by eating away at whatever is in their path.  This includes your skin if any were to splash on you.  Their vapors are also harmful to your respiratory system.

Using chemical drain cleaners as a preventative is not a good idea.  Especially if you have a septic tank as the chemical drain openers can kill off all the beneficial bacteria for the efficient working of the tank.  Also, do NOT use a plunger after using chemical drain openers, as this is an invitation to splash yourself with toxic, burning chemicals.

Regularly running boiling water down the drain is usually the safest and best way to keep your drains clear and running well.  Since greasy deposits are a major cause of clogged drains, try not to pour grease down the drain if you can help it.  Instead, let the grease cool and become solid, then dispose of in a baggie, seal it and throw it in the trash.

A non-toxic recipe to open and clean your drain:  7 ounces of baking soda, 3 ½ ounces of table salt, and 7 ounces of vinegar.  When the alkali (baking soda) meets the acid (vinegar), they will bubble furiously, pushing the abrasive salt through the drain.  All 3 ingredients will work to remove deposits from the drain and clear it out.  After about 20 minutes, pour boiling water down the drain to flush it clear.