DIY & Home Improvement

Locating the clog determines how you treat it.
Repeated treatments with mild acid (like liq plumber) is a waste of money if the clog
is far down the drain. By the time the acid reaches it, it's even too dilute to do much aside from making a small hole in the clog.

Had a similar problem with a kitchen drain, finally rented a motorized snake and reamed it out
way down the pipe. Fix has lasted for years with a little help from some serious sulphuric acid added on occasion.

Clogs often happen when two drain lines (like kitchen and bath) meet and gunk builds at the junction.

Air and water pressure are good ways of working it too.
The hardware store will have a thing called a "Drain King". It's a rubber tube with a small hole at one end and an attachment that fits a garden hose. You disconnect the drain under the sink and stick the drain king into
the pipe and turn the water on. The rubber bladder swells to the pipes diameter, sealing it and then forcing pressurized water into the pipe. This is the cheapest solution you will find. Drain kings come in a couple of sizes for less than a bottle of weak acid.