Kitchen Sink Plumbing Modification
Posted by Wayne
I posted some time back about how when I installed a new sink in our kitchen it was so much deeper than the old sink that I had to turn the p-trap backwards to make the plumbing work at the existing drain heights. The problem was that due to the depth of the sink the drain for the garbage disposal was now only a hair higher than the drain coming out of the wall. It really needs to be at least several inches higher to install the p-trap the right way.
I suspected that the only issue I could have with the p-trap being on backwards would be that because the “u” of the p-trap was now deeper than normal it might have some issues keeping itself clear of waste and the sink would start smelling. It turned out that the backwards p-trap functioned just fine. The issue was in the way the p-trap connected to the rest of the plumbing. In short, it was barely hanging on. It’s just wasn’t a tight fit.
I first noticed a small leak in the connection after I (or my wife) bumped the plumbing underneath the sink while reaching under there. I realized that this was a problem and it could really come loose and leak for a while before anyone noticed, but we were trying to get the kitchen finished in time for a party we were having and I didn’t want to start another project. As a short term fix I reconnected the p-trap and placed a bucket underneath as insurance against any leaks.
The day before the party my wife had a cleaning lady come to the house to get everything sparkling fresh. That evening we came home to find a major issue underneath the sink. The cleaning lady had evidently bumped the plumbing reaching under the sink hard enough to completely disconnect the p-trap and had used the sink all day long. Thank God I had put that bucket under there! It was a lucky coincidence that she had only run the water enough to fill up the bucket and it had only just started to overflow.
Party or not, I had to fix the issue right then. As previously threatened (see the post by clicking here), I would simply tranform my plumbing arrangement to that which is used on the East Coast (and Michigan, according to my friend Mike).
In Colorado we use a two drain arrangement where the top drain is used for the sink and the bottom drain is used for the dishwasher. I would simply cap off the top drain, connect the dishwasher to the garbage disposal, and use the bottom drain as the sink drain. It was either that or rip into the wall behind the cabinet to change the top drain height so I could use a p-trap the normal way.
I pulled the dishwasher drainage hose out of the drain to see how it would connect to the garbage disposal. I knew that there was some sort of plug that I’d have to punch out of the garbage disposal to use it as the dishwasher drain. I couldn’t get up there to see it so I held the camera and took a picture to confirm it.
I realized that I’d have to completely remove the garbage disposal from the sink to punch out this plug. Not only is that quite a bit of work in itself, but the garbage disposal is hardwired electrically and that would be a pain to disconnect as well. In a nutshell, I wasn’t going to take the darn thing off of there because it was too much work and there were other options.
I decided to cap off the top (original) drain, cut the dishwasher drain pipe and install a 90 degree wye fitting at an appropriate height and use that as the sink drain. I’d then reinstall the length of dishwasher drain on top of the wye and continue to drain the dishwasher in the same manner. See the image below for visual descriptions.
Before
After
After
The wye is now a permanent part of the dishwasher drain, but the cap simply screws on and I was careful to make sure everything is reversible in case I or a future resident wanted to change it back around. While technically this arrangement isn’t to Colorado code, it is completely functional and I have no worries about leaks or a backwards p-trap anymore.
The upper p-trap actually doesn’t even serve a purpose other than it is easier to connect to the new drain by using it than not using it. I guess if somehow a clog developed it would be certain to happen in the upper trap which is a thinner pipe than than the lower trap, and I could still take apart the upper trap to investigate if I needed.
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