When installing a dishwasher, it is crucial to connect the drainage system properly. Similarly, if your dishwasher is not draining properly, the pipes were probably not installed in the correct position. The question that often arises is, should the dishwasher drainpipe be level or curved?
A dishwasher drainpipe should be curved into a high loop in line with the sink bowl, with the end connected above the P-trap. The water pumps upwards when draining, and the upward loop stops water from the sink or garbage disposal from going into the dishwasher. A u-clamp can hold it in place.
Not connecting the drainpipes correctly, using incorrect-sized pipes, or not using the proper materials can damage your entire under-sink connection and damage your dishwasher by flooding or not allowing proper drainage.
Should A Dishwasher Drain Be Level Or Curved?
The most straightforward answer is that the dishwasher drainage system should always be curved. While you can leave it leveled in the technical sense, it is absolutely not recommended and even forbidden in most states in the USA. A leveled drain can cause pipe blocks, dishwasher flooding, sink drain blocks, damage to the garbage disposal, and explosive releases through the air gap.
Dishwasher manuals always provide instructions and guidance on correctly connecting the drain system. Diagrams will also show the pipes curved in an upward direction. There is an art to that methodology.
Why Should The Dishwasher Drain Be Curved?
A dishwasher drain should always be curved upwards – called a high loop installation – with the loop in line with the sink bowl. The pipe should also be connected to the plumbing before/above the P-trap. It should not be on or after the P-trap. The loop should remain at the top and secured, so it does not fall or bend and change position or tug at the connection ends.
There is one primary reason for the curved method, which is of utmost importance. If the pipe is not curved in a high loop and allowed to hang down or left leveled, the sink and garbage disposal water can run into the dishwasher draining pipe and enter the dishwasher. That causes drainage issues, flooding, and bad sewage gas smells.
Additionally, the dishwasher pumps water upwards when it drains, so there is no concern of water not draining correctly or flowing back because the pipe is turned upwards. Unless the dishwasher is old or the pump is not working well, there might be slight issues which can be sorted by plumper or by replacing the old pipes and pump with new, fresh ones.
Connecting The Dishwasher Drain To The P-Trap
After ensuring the dishwasher drainpipe is in the position of a high loop, connect it to the plumbing system above the P-trap. If you connect it to or below the P-trap, wastewater and gunk from the sink and garbage disposal will enter the pipe. Connecting it above makes it too high for drain water to flow into the dishwasher drain.
Height Of The Curved Dishwasher Drain
Many people wonder how high should the dishwasher drain be. Should it reach the top of the cabinet, or as long as it is upwards, the height won’t matter? The fact is that height matters in most cases. The loop must be high enough to prevent wastewater from running into the dishwasher. If water does enter that pipe, if the loop is high enough, it will fall back. That is the aim.
The height of the loop should be around 33-43″. It will depend on the size of your space. If you have open space next to the sink within the cabinet, the best way is to allow the loop to be in line with the sink bowl, close to the countertop. If the bowl takes up all the space, place the loop immediately below the sink against the cabinet’s side.
How To Secure The Dishwasher Drain Loop?
Once you curve the drain in position at the top, you want to ensure it stays in place. If it falls downwards, it will allow drain water to run into it. If it bends, it will cause pressure which can cause blockages or bursts. So, how do you secure the dishwasher high loop drain?
Here are three techniques that are easy for even a novice to install:
Use a U-Clamp attached to the cabinet.
A u-clamp is a metal tool in the shape of a “u,” which helps secure plumbing pipes. You can attach the clamp to the side of the cabinet (recommended or under the countertop (ensuring it will not damage or go all the way through).
Hang it with a zip tie and a screw.
A zip tie is an easy and affordable method. You can place a screw into the side of the cabinet at the height you want the loop to be. Place the zip tie loosely around the drainpipe. Hang the zip tie from the screw. That way, your drain will remain at the top in the curved position.
Make the pipe hole at the top of the cabinet.
Instead of cutting a hole at the bottom of the cabinet for the drainpipe, cut one on top. That way, your pipe will run upwards, curve at the top, and run down to the plumbing side under the sink, and remain in that position. Try to make the hole as high as possible when using this technique.
Is An Air Gap Required For Dishwasher Drainage Systems?
An air gap is a requirement in some states, such as Washington, Minnesota, California, and Hawaii. The air gap is installed above the sink, next to the tap, and prevents accidental backflow of contaminated water. For plumbing systems with air gaps, connect the dishwasher drainpipe to the smaller leg of the air gap tube and secure it with hose clamps.
In states that don’t require air gaps, the drainage pipe will connect directly to the plumbing system of the sink and should be above the P-trap.
Can A Dishwasher Drainpipe Be Directly Under The Floor?
According to most states in the US, it is not allowed to run the dishwasher drainpipe directly under the floor. It is required for the drain system to be above flood level. Dishwashers drain upwards, so the pipe needs to run upwards to prevent function issues. The curved high loop also prevents wastewater from running into the dishwasher.
Conclusion
The dishwasher drain system should always be curved to prevent wastewater from the sink and garbage disposal from entering the dishwasher. The curve should run at the top in a high loop and be secured to avoid it from falling downwards.
