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Two Drains Under Kitchen Sink [Explained]

It’s unusual to see two drain lines under one kitchen sink. It’s confusing to work on them. Not to mention how it’s tough to find plumbing replacements for them.

But are two drains under the kitchen sink necessary?

Two drains for one kitchen sink are uncommon these days. One of the drain lines works as garbage disposal. The other works as a vent. Two drain lines are not necessary for a single sink. Most people prefer to convert their double sink drain line to a single drain.

That was only a small part of the whole discussion. We’ve explained more about this topic in detail for you.

What are you waiting for? Let’s jump right in!

What Is the Purpose Of Two Drains Under Sink?

Two drains under one sink are not something you see in today’s households. In old households, it was common but not anymore. 

But two drain pipes under one kitchen sink are unnecessary now. In the modern plumbing system, a single drain can take care of your sink. But be careful not to get your drain bladder stuck in there.

In two drain line systems, one of the drain lines disposes of garbage water. The other one is installed as a vent. 

By the plumbing rules, the left drain is used as a vent. Comparing it with a single drain line system this vent is not needed anymore. The single disposal line is enough.

Two drain systems are uncommon even for double sinks. The repair process is also troublesome. You can choose to cap the vent line like how capping galvanized pipe works. But changing them to a single drain system is a much better decision.

How to Shift Double Drain To Single Drain?

Changing the old two-drain system to a single drain is more advantageous. It’s gonna save you from a lot of plumbing hassle. It’ll also give you some free space under the sink. 

Here are some tools that you’re gonna need for this project-

  • Adjustable wrench
  • Screwdriver
  • A garbage disposal
  • Jigsaw
  • A bucket of bowl
  • New PVC pipe set for the sink drain

Have all you need? Let’s get started!

Step-1: Disconnecting Old Drain Lines

Shut off the water supply when you’re working first. Disconnect the pipe from the garbage drain line of the wall now. Do it for both drain lines. 

Detach the joint from the pipe to the disposal hole as well. Use a wrench if necessary to untwist and pull it off. 

Disconnect the other side of the pipe that’s connected to the sink now. You’ll see a screw that’s holding the pipe with the sink’s flange. 

Untwist the screw to disconnect the pipe. Place a bucket underneath to catch any remaining water in the pipe.

Step-2: Dispose of The Old Sink Flange

You’ll need a compatible-sized sink flange for the new PVC set. If you wish to keep the old flange, buy the same sized inlet. 

But it’s best to change the flange along with the drain line. That’s why while buying the PVC set make sure you’re getting a new sink flange.

Popping out the old flange is easy. Just unscrew the nut and pull it off from the sink. Once done, apply some abrasive cleaner to a rag and clean the revealed place.

Step-3: Install New Sink Flange

You’ve to place all the parts of the flange in one-by-one order first. The sink flange has a rubber gasket that works as a sealer. It goes under the round metal dish. If your flange is missing the gasket, you must use plumbers putty.

Put the flange on the sinkhole. Attach the paper gasket from under the sink after that. Attach the black threaded bracket under the paper gasket too. 

Now comes the mounting hardware. Join the mounting hardware and the rubber cushion back to back.

Step-4: Installing Garbage Disposal

Using a kitchen sink garbage disposal is the best to secure your drain connection. If you’re already using one, you can reconnect it with the flange. But make sure it’s free from the usual plumbing problems of the garbage disposal.

Some garbage disposals are ready to be plugged in. others are to be plugged manually. Read the manufacturer’s guidelines to know how your garbage disposal works. 

Remove the dishwasher plug if it has to be connected to the dishwasher line. You can simply use a screwdriver to knock it out of the place.

Connect the garbage disposal with the sink flange now. Twist the device to tighten the connection properly. 

Step-5: Install The PVC Connections

The whole set of PVC pipes should be in the purchased set. We recommend these products for you-

Product 1
Product 2

Got them? Let’s use them then.

Some of the pipes might need to be cut to the required sizes. You can use a pipe cutter or a jigsaw to cut them. Use the type of jigsaw that cuts household ductwork.

Once finished, attach the PVC inlet to the garbage disposal plug. Connect the dishwasher line to the designated hole on the disposal. Check for any water leakage in the PVC connections now. Hopefully, everything is working just fine.

Step-6: Block The Other Drain Line

The other drain line shouldn’t be kept open. It could lead to insect infestation if left open. Use plastic boards or even better if you put cement to block it.

And that’s how to convert a double kitchen drain to a single drain system.


Question: Is a double sink better than a single kitchen sink?

Answer: Both double and single kitchen sinks have their own advantages and disadvantages. A double sink is good for the busy sink area. Otherwise, it’s unnecessary to get a double kitchen sink.

Question: Can a double kitchen sink use one drain line?

Answer: Yes, a double kitchen sink can be adjusted with one drain line. Use tee fittings, extension pipes, and special valves to adapt to a single drain.

Question: How to unclog the kitchen drains?

Answer: Pour a cup of boiling water down the sink. Put 1 cup of baking soda and 1 cup vinegar consecutively afterward. Wait 5-10 minutes then pour 1 cup hot water again. The drain shall be unclogged.


We’ve reached the end of our discussion regarding two drains under the kitchen sink. Hopefully, this piece of ours was helpful for your plumbing project.

Until next time!