There are many ways to clean a drain without exposing yourself and the environment to toxic chemicals.
One such method is to use a sink plunger. It should always be the first step you take before pouring anything down the drain. However, before you start plunging it is important that you block other drains that lead into the same line and fill the basin with water. The plunger must be pumped and then jerked off of the drain. This process can be repeated as many times as necessary in order to unblock the drain.
If the plunger does not do the trick, a non-toxic drain flushing formula can be created with simple household supplies. A cup of baking soda should be poured into the drain, and then followed by a cup of vinegar. The two ingredients will mix and create a foaming action to dislodge whatever is blocking the drain. After the fizzing stops, boiling hot water should be poured down the drain to disperse the foam.
This may not work on seriously blocked drains, but it often works on minor blockages.