Basement Drain Backing Up? Here’s How to Unclog It
Clearing a clogged drain line requires a little more work than most household clogs, but with a little know-how, you can fix the problem yourself.
If the plunger and the snake fail, you probably have a big clog somewhere in the drainpipe. Here's how to locate the clog and grind your way through it.
- Allen wrench
- Cold chisel
- Pipe wrench
- Safety glasses
- Shop vacuum
- Slip joint pliers
- Expansion plug
- Hand cleaner
- Plastic cleanout plug
- Teflon tape
Clogged drains are always a hassle, but some, clogs are easier than others to fix. A plugged up P-trap under the kitchen sink or a stopped-up toilet, requires only a wrench, a plunger and a little elbow grease to unclog.
But sometimes the clog is deep in the drainpipe and requires more work and extra-powerful tools to root out. We’ll show you how to find and clear out these clogs, which are often hidden in the drain system under your floor.>
Video: How to Unclog a Drain
Under-Floor Drain System
The job of clearing clogs in the larger drain lines found under the floor isn’t for everyone. In the first place, you’ll spend about $50 a day or more to rent the large drain-cleaning auger required, and you have to be strong enough to heft the machine and to wrench loose those old, corroded cleanout plugs. Then there’s the mess, and the half-day you’ll spend running for rental equipment and miscellaneous plumbing parts. So why would anyone in their right mind attempt to clear out under-floor drains?
However, it’s like to cost more to have a professional plumber come to your house, and their schedule might not always sync up with yours.
Keep in mind, however, that some clogs require the services of a pro. Don’t hesitate to call a pro if you suspect that the main drain to the street is clogged by tree roots or caved-in pipes.
Project step-by-step (14)
Find the Clog
The first step in clearing a clog is locating it. This often takes some trial and error, but here are a few pointers to get you started. If only one fixture is clogged, the problem is either in the trap or drain line leading from that fixture. If a group of fixtures is affected, look for the clog in a location downstream from where their drains join.
The photo above shows the drain system under the floor of a typical house. Notice that a clog in the location shown would affect the laundry and kitchen drains, but not the upstairs bath that drains into the main stack. A clog in the larger main drain would cause all the drains to stop working.
As many of us have discovered the hard way, a clog in the under-floor drain system often results in wastewater backing up onto the floor through the floor drain. To prevent this backup, many floor drains are fitted with an insertable backflow preventer that allows water down but not up.
Clear a Floor Drain Trap
Remove the backflow preventer to gain access to the floor drain trap for cleaning. Drive a chisel against one of the notches in the retaining ring, turning it counterclockwise to unscrew it.
Clean Out the Trap
Vacuum out sand and dirt with a wet/dry vacuum. Loosen stubborn dirt or snag and retrieve other yucky stuff with a coat hanger or small, hand-powered drain snake.
Remove the Cleanout Plug
Unscrew the cleanout plug in the side of the floor drain with a pipe wrench, slip-joint pliers, or as a last resort, by chiseling it out with a cold chisel.
Clear the Drainpipe
If cleaning the fixture trap doesn’t solve the problem, and you’ve determined that the clog is in one of the under-floor drains, then you’ll have to rent a drain-cleaning machine. With it, you can punch through the clog, snag and retrieve an obstruction, or cut through roots or stubborn clogs.
Unplug the drainpipe leading from the floor drain by using a 1/2-in. cable inserted through the cleanout opening. Start with a general-purpose drilling or retrieving tool attached to the cable, and complete the job with a finishing tool.
Opening Stubborn Plugs
The first thing you have to do to work on an under-floor drain is to remove the cleanout plug. Removing a plug from corroded steel or cast iron fitting is a real chore. Try using a pipe wrench with a steel pipe slipped over the handle to increase leverage. If this doesn’t work, you’ll have to resort to chiseling.
Drive corroded cleanout plugs counterclockwise using a cold chisel and heavy hammer after squirting them with penetrating oil. If this doesn’t work, break out the plug with the hammer and chisel, being careful not to let any pieces fall into the drain. Wear gloves and safety glasses, and be prepared for a possible flood of wastewater (yikes!).
Note: Removing the cleanout may release a flood of backed-up wastewater, so be prepared with buckets and rags, and stay clear.
Rent a Drain-Cleaning Machine
Before you head to the rental store, try to determine the location of the clog, or be able to describe the symptoms.
You’ll also need to know what size auger to rent. Determining that is based on the size of your drain line. Smaller drain lines, from 1-1/2 in. to 3 in. in diameter, require a 1/2-in. cable. Larger main drains require a 3/4-in. cable.
Ask the rental agent to recommend the correct machine and show you exactly how to use it. Also, ask for safety instructions. Inspect the machine to make sure the motor and pulley are covered with a guard. Ask the rental agent to test the built-in ground fault circuit interrupter (GFCI), check the cord for fraying or wear, and make sure the cable is not bent, kinked or tangled. Ask for an assortment of cleaning tools and a description of their use.
These machines are very heavy; a large machine with 100 ft. of 3/4-in. the cable can weigh 215 lbs. You’ll need help getting it in and out of your car and into the house.
Some rental machines use a cable that’s dual-wound and has a self-feeding feature. Ask your rental dealer for safety and operating instructions.
Connect a cleaning tool to the cable. Use the starting drill to bore through a clog, the retriever to snag rags or other items, the grease tool to cut through grease and soap and clean up the sides of the pipe, and the root saw to cut through roots.
Operating a Drain-Cleaning Machine
These machines are powerful, and dangerous if safety precautions aren’t followed. Read and follow the instructions provided with the equipment.
Position the machine 2 to 3 ft. from the cleanout opening, plug it into a grounded outlet or 12- or 14-gauge grounded extension cord, and make sure the switch on the motor is in the “Forward” position. Put on heavy leather gloves and safety glasses and make sure you aren’t wearing any loose clothes, belts or jewelry that could become entangled in the cable.
Position the foot-operated switch where you can step on it while you’re feeding cable into the drain. Practice starting and stopping the machine with the foot switch to get the hang of it.
Feed in the Cable
Keep both hands firmly on the cable and slowly feed it into the pipe as you stop and start the motor with the foot switch until you can’t push it any further. Feel for an increase in cable tension and listen for the motor to slow or the built-in safety clutch to slip. All of these indicate you’ve reached a clog. Stop immediately when you sense a change.
Reverse to Relieve Tension
Flip the switch on the motor to “Reverse.” Then use the foot switch to run the motor in reverse for a few revolutions of the cable cage. This will relieve tension that may have built up in the cable when it hit the clog. Switch the motor back to “Forward.”
NOTE: The only other time you should reverse the motor is when the cable gets stuck and will not turn in the forward position.
Take Your Time
Chew slowly through a clog by following these steps:
- Tighten the lock bolt that secures the cable.
- Depress the foot switch, running the machine in “Forward” while you hold the cable.
- Loosen the lock bolt, feed a little more cable into the drain and retighten the bolt.
- Repeat this process until you cut through the clog.
Replace the Cleanout Plug
After you’ve conquered the clog and it’s time to replace the cleanout plug, use a plastic rather than a metal plug, and don’t forget to use Teflon plumbing tape to seal the threads.
If the cleanout fitting is too damaged or corroded to use a threaded expansion plug as shown. Install the expansion plug. Push the plug into the cleanout fitting, and tighten the thumbscrew or Allen bolt in the middle of the cover to complete the seal. Plumbing suppliers also carry a variety of plugs and couplings that will solve the problem.
If you have the time and energy after boring through the clog, clean the sides of the pipe by attaching a finishing tool to the cable and running the full length of the cable down the drain. Then use a hose to run water down the drain as you retrieve the cable. The water will flush the debris down the drain and rinse gunk off the cable as you
reel it in.