Clogged drains are just part of the joy of indoor plumbing. The good news is that you can troubleshoot the issues and prevent them from happening again, including chronic problems. But to get there, we'll need to get into what causes drain clogs in the first place.
Troubleshooting: Remove and clean the drain stopper. Next, try using the humble drain plunger, keeping in mind to block the overflow drain in the tub or sink. If that doesn't work, remove the drain elbow joint and clean it out. Clean drain stoppers routinely to prevent clogs and use a hair strainer drain-cover to trap hair before it goes down the drain.
The best preventative for keeping your toilet free from clogs is to only put in waste and paper that readily dissolve in water. Regular cleaning will also keep water flowing smoothly.
Troubleshooting: Tackle kitchen sink drains like you tackle bathroom sinks. Start by running very hot water down the drain to soften the clog, followed by a dollop of dish detergent and then more hot water. Wait a few minutes, and then use a plunger and repeat the hot water. If you still have no luck, you might want to move onto a chemical drain opener. Again, use caution.
In the future, dispose of large amounts of kitchen grease and oil by letting them solidify. Scrape the mess into a plastic bag, seal it, and throw it out with the garbage. Small amounts of oil (less than one cup) should be thoroughly diluted with hot water and dish detergent before being poured into the sink.
If you are constantly plagued with clogged or slow drains, have a plumber inspect the plumbing to determine if the drain line was properly designed and installed. Both drain pipe venting and slope effect how well drains work.
Meanwhile, drain pipe slope determines how well water carries waste to the sewer line. If there's too much slope, water can run too fast and leave waste material behind. Over time, the buildup forms a blockage. If the pipe slope doesn't have enough slope, then the water and waste pool in the pipe. Some waste will settle out and, again, form a blockage.
Troubleshooting: First, check that nothing is blocking the vent pipe opening on your roof. Sometimes birds or other animals build nests on top of un-enclosed vent pipes for warmth. Also, check under sinks for gulp valves. Gulp valves are typically mounted at the end of a drain line and look like a plastic cap from a can of spray paint. The valve prevents sewer gas from escaping the drain line but lets air into the vent pipe when there's enough suction. If you fill the sink with water and then drain it out all at once, you should hear air getting sucked into the gulp valve. If not, the valve might need to be replaced. Also, if there is a constant odor of raw sewage in your home, contact a professional plumbing service immediately.
For slope problem, any blockages will first need to be removed with a plumbers' snake and the pipe flushed out with water. A new pipe set at the proper slope to carry sewage away more effectively should then be installed by a professional plumber.
Note: These tips are suggested as general practices. However, actual results may vary.