This method assumes you have PVC or plastic piping underneath your sinks but it can be used with metal pipes as well. You will require a pipe wrench with metal piping to loosen the connections. This technique is primarily for clogs beyond the ones in the piping beneath the sink but before the main stack pipe. These clogs are notoriously stubborn.
Determining the location of the blockage
How will you know where your pipes are blocked up? If your bathroom sink, toilet, or tub is obstructed and they are on a different branch, it is probably the main stack which is clogged. This is highly unusual. The main stack is the large diameter metal pipe running horizontally from the basement up to the other floors of your house. Bathrooms are usually placed beside the main stack.
To check if there is a block beneath your sink, look underneath for a curvy shaped piece at the bottom call the trap. It traps water at the bottom of the piece at all times to act a barrier to sewer gases. It also can trap other waste residue which can block your pipes. If you disconnect trap and check that it is clear, most likely the clog is in a branch pipe beyond the sink. To disconnect, simple unscrew the slip nuts connecting the trap on both its ends. The trap usually jams up more times than not.
The double sinks in kitchens occasionally clog up. The problem with double sink clogs is that it almost immediately rules out effective plunging because of the requirement to not only seal but hold the intense pressure against the drain hole of the sink which is not being plunged. Using rags or holding down the drain plug down will still let air pressure escape. Even using a helper to plunge the other sink won’t work. When your plunger is going down, your helper’s plunger will be going up and vice versa.
Here is a unique solution. Rearrange the plumbing underneath for use by only one sink temporarily to apply a high amount of pressure on the clog. There are two ways this can be accomplished. Both methods involve one more PVC piece and are easy to do.
Let’s go over what’s under your double sink. With most double sinks, there is a straight horizontal piece called the tail-piece which connects with the strainer that is in the center of the sink. Think of each of your sinks having a tail. Each sink has its own tail-pieces which are the same length. One of the sinks will have a sideways T-shaped piece (tee) that connects with the tail-piece piece at the top. The T-shaped piece will also connect on the bottom to the trap. At the side, the T-shaped piece will connect with a horizontal pipe (arm) which connects with the straight piece of the other sink’s drain hole.
Let’s think in terms of streets. If the two drain-holes are houses parallel to each other but some distance apart, one is house A the other is house B. Each one has a road the same length extending straight from the front door (tail-piece). After the straight extension, House B has its road turn 90 degrees toward House A’s road (arm). House A’s road continues straight after the extension but has an intersection with House B’s road. That’s where the tee is.
The easy method is to go to your hardware store and purchase an item called a slip cap. It should be the same diameter as your current pipe. Actually it will be slightly bigger but the package diameter label should match the pipes underneath your sink. Once you have this item, place a bucket or dish pan under the tee/arm connection and disconnect the arm from the tee. Let the water drain. You may also need to loosen but not disconnect the arm from the tail-piece to allow it to swing out of the way. Then simply screw on the cap to the tee. You now have a way to plunge without worrying about pressure leaking from the other drain hole. The connection with the second sink has been eliminated.
The other method would be to purchase an item called an extension. This would simply extend the tail-piece to connect directly with the trap without using the tee. For this method, disconnect the arm as before. Then disconnect the tee with the tail-piece. Finally disconnect the tee with the trap. Place the extension above the trap and connect it with the trap. Also, connect the tail-piece with the extension. This method is better at holding pressure than the previous arrangement because there is one less connection and one less diversion for the water to be routed. However, it does require a couple more steps. Most extensions do allow for adjustment in length. The top part of the extension will have a couple inches of wider width to fit over the tail-piece and adjustments can be made by sliding it up and down over the tail-piece.
When installing the new pieces, be certain the slip nuts and cap are threaded on straight. Also make sure the washers are aligned correctly. When you first plunge, you may notice minor leaks at the connections. Simply tighten by hand again.
Congratulations, now you can plunge effectively and easily remove the clog. You can also use other pressure methods such as an air-gun type device that shoot powerful bursts of air over the drain-hole and into the pipes. Yes someone did invent a device like that so you can literally take aim and fire at blockage your pipes.
Once the clog is clear, reverse the method to replace the pipes back to the original formation. Disconnect your extension and replace it with the tee. Connect the arm, tail-piece and trap. Don’t forget to tighten the arm with the other tail-piece. For the cap method, simple unscrew the cap and tighten the arm connections. Save the cap or extension for future use.