Drain clogs are troublesome, but they often go away with with a little plunging and flushing with some household cleaning agents, such as vinegar and baking soda, and hot water. Persistent clogs are another matter. When greasy, hair-infused sludge accumulates in the P-trap, the branch waste lines or the sewer, you need the cavalry -- a water jet, an auger and maybe even a camera, so you can see what's going on. In some cases, you'll have to do some disassembling to get things cleaned out.
Sludge in a Sink Drain
When water backs up in a kitchen or bathroom sink, and plunging doesn't have any permanent effect, solid material may have collected in the bottom of the P-trap, creating a constriction that attracts more material. A sink auger may help, but its rotating cutting heads are more effective against mid-pipe clogs. The best way to clean the the pipes under the sink is to disassemble them and wash them out manually:
Unscrew the nuts holding the P-trap to the sink tailpiece and the waste pipe in the wall. If you can't do this by hand, use adjustable pliers.
Remove the P-trap carefully; hold it over a bucket and invert it to empty the water. Pull out the sludge and debris you can grab with your fingers, and drop that into the bucket.
Take the trap outside and wash it out with the jet from a garden hose.
Bring the hose indoors -- if it won't reach the sink, use an adapter to connect it to the sink faucet. Spray water into the waste pipe. Spray carefully at first, in case it backs up, and then turn up the pressure to give the pipes a good cleaning.
Insert an auger into the waste opening to clear blockages that the water can't clear. Once the auger pushes its way through the clog, spray with water to push the clog into the sewer.
Reassemble the trap after you've finished cleaning the pipes.
Sludge in Waste and Sewer Lines
If several drains in your house run slowly or frequently back up, and you're sure the vents are clear, you may have a sludge accumulation in one of the main waste lines or in the sewer. You can usually pinpoint the approximate location by noting which drains are running slowly. Find the nearest clean-out fitting, and remove the cap with a pipe wrench. Insert a drain auger into the clean-out and feed the auger in the direction of the clog. Once the auger contacts the clog, crank the handle to work the head through the sludge. Prepare for a mess when you retract the auger.
Backups in sewer lines aren't always easy to pinpoint -- you may need to hire a plumber to insert a camera into the pipes to see what's going on. The plumber can help determine if tree roots are responsible and plan a strategy for clearing the pipes. In some cases, a high-powered water jet may be a better choice for clearing the pipes than an auger.
The best way to prevent drain clogs is to watch what you put in the drain. Avoid putting grease, hair, stringy vegetables, or aggregates like sand or tile grout that can collect in the bottom of the P-trap down the drain. Regularly pouring an enzyme-based drain cleaner into your drains ensures that grease and oils won't collect on the sides of the pipes.