Is it better to use a whole bottle of drain cleaner in one shot or use half a bottle twice?

Answer 1

It depends on the severity of the clog, the depth, the ability of the cleaner to reach the clog is the key, if it just sits behind the clog it's wasted. Kitchen sinks generally have grease buildup which requires more cleaner, if you were trying to unclog a bathtub which had slowly clogged over a period of time, you might leave the cleaner overnight, if the pipes are sound. In all circumstances safety is the first and last consideration. Simple clogs today can be effectively treated with air pressure, there are various inexpensive devices that push the clog with compressed air. Treating the drains regularly with home remedies is more effective, vinegar, baking soda, bleach, keeping grease in containers, etc.

Answer 2

Go to home depot and get a plunger or a small drain snake
After getting it open pore LOTS and LOTS of boiling water down the drain to help remove the grease / sludge build up

Be care full what goes down the drain

And it is good monthly preventive maintenance

Answer 3

You should follow the directions on the bottle