We are in the midst of installing a new kitchen.

Our old kitchen has the standard double sink and adjoining dishwasher all going to a single p-trap in the sink cabinet.

One of the things that really bothered me with this arrangement was the GE dishwasher drain noise that came up through the sink drains. It was significantly quieter if I put the drain stoppers in the sink - but it was a nuisance to remember to do this all the time.

We have the same layout in the new kitchen but I was wondering about installing two traps in the new sink cabinet: one for the double sink and a second one for the dishwasher.

Other than it looking strange, is there any reason why I shouldn't do this? Is there a better was of solving the noise issue?

There is a way to install a second trap that will cut down on the noise and that sounds like what your main objective is. Install the second trap and then drain the dishwasher into the trap with a direct connection. From the connection to the trap make sure that the dishwasher hose is looped up as close to the underneath the sink cabinet and secure it with a hanger of some kind.
I do not recommend this way but some of the other plumbers do. One reason I don't agree with it is because of a cross connection, that is when there is a possibility of dirty water being pushed or syphoned back into the dishwasher.
Another reason I don't like this way is as your dishwasher is draining and it starts to fill again as the pump is still running, like in the rinse cycle and then into the second wash the water going out of the washer can cause a syphon and your dishwasher will not completely fill for that second wash. Most others will say this can not happen or that it does not matter. Good Luck.

Thanks for your response.

I just checked with our local plumbing inspector as he will be inspecting it anyway. The answer is 'no', I can't do this without a separate connection & vent. I can't have two traps on a single line as one may siphon the other out.

I'll hook it up the standard way. If there is too much noise then I'll tie the dishwasher into a new trap that I can install in the basement under the kitchen floor.

" I can't have two traps on a single line as one may siphon the other out."

That's odd! The only way one trap and pull water out of another is if they were in series with each other on the same line and the first trap was unvented.
We have always came out of the wall with one stub-out and wyed off to a trap for the disposal that the DW drains into and a separate trap for the sink tub. Since they both run into a common vent stack we have never lost a trap seal due to suction. Regards, tom

Thanks for your response.

I just checked with our local plumbing inspector as he will be inspecting it anyway. The answer is 'no', I can't do this without a separate connection & vent. I can't have two traps on a single line as one may siphon the other out.

You could have two traps if you use a partition cross.

We have always came out of the wall with one stub-out and wyed off to a trap for the disposal that the DW drains into and a separate trap for the sink tub. Since they both run into a common vent stack we have never lost a trap seal due to suction. regards, tom

The IPC allows two traps on a single trap arm?

If you're going to go to all that trouble, why not join the two compartments of the sink with a continuous waste and put the dishwasher on it's own trap?

It sure would go a long ways towards eliminating the frequent complaints of excessive noise from discharging a DW into the disposal.

I have a single stub out of the wall as Tom described.

While I agree that it is unlikely that one trap will siphon out the other, the reality is that the inspector will not pass it. My options are limited without redoing some of the drywall that I just finished. I should have asked my question a few weeks ago before I did the kitchen rough-in!

Thanks, all.