I finally wrapped up redoing the plumbing under my double-bowl kitchen sink and I’m acutally pretty relieved it’s not leaking. I spent most of the time worrying about the disposal side becasue that horizontal connection pipe just didn't look right to me initially. I was convinced it needed a steeper drop to drain properly, but after looking into it, the horizontal run into the main T-junction is actually standard for these setups. Getting the dishwasher drain line hooked back into the disposal was a bit of a pain since the hose was stiff, but it's snug now. I also made sure the copper supply lines weren't getting knocked around by the new PVC layout. It’s a tight fit with the P-trap heading straight into the back wall, but everthing clears the electrical outlet for the disposal. It feels good to have that project behind me and see everything flowing smoothly without any drips on the cabinet floor.
Just finished redoing the kitchen sink drains and learned a few things about disposal runs
Sep 21, 2026
Last reply: 1 day ago
3 Replies
I went trough a similar headache with my Insinkerator setup last summer. I've always worried about the horizontal waste arm backing up if it isn't sloped perfectly, but as long as you have that 1/4 inch per foot drop, it usally works out fine. I acutally had to swap out my center outlet tee for a directed baffle version beacuse I was getting some nasty crossover flow from the non-disposal side.
For the dishwasher hose, I found that warming it up with a hair dryer for a minute makes it way easier to seat on the nipple. I also ended up installing a high loop even though my manual said it wasn't strictly required; it just gives me peace of mind against dirty water siphoning back into the machine.
I've had the same concern with copper supply lines. On my last sink job, I used some foam pipe insulation around the pipes where they got close to the PVC just to prevent that annoying clinking sound when the disposal vibrates. It’s a small thing, but it helps when the clearance is that tight against the back wall.
I had a similar setup with a double-bowl sink last year, but I acutally ended up regretting using the stiff factory dishwasher hose. After about six months, the vibration from the disposal started causing a tiny weep where it connected to the inlet nipple. I switched over to a high-loop with a more flexible braided line and a stainless steel hose clamp instead of those spring tension clips. It made it much easier to tuck everthing behind the supply lines without putting tension on the disposal housing.
Also, keep an eye on that tight fit near the electrical outlet. I actually had to relocate my GFCI box slightly to the left beacuse my P-trap assembly would sweat during heavy use in the summer, and I didn't like the condensation being that close to the wiring. If you have enough room, slipping a bit of foam pipe insulation over the cold water side can prevent that moisture from dripping near your electrical.
Oh man, seeing a dry cabinet floor is the absolute best feeling ever!! I just started DIYing my own home repairs and it's like a giant puzzle under there. Since you mentioned the electrical outlet being so close to the P-trap, does that ever get sketchy with moisture or code? Also, totally random question, but has anyone here tried those touchless motion-sensor faucets? I’m dying to get one for my kitchen but I’m worried the sensors die after a few months and leave me with no water!
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