Finally cleared that brutal kitchen sink blockage and found the culprit

I had a nearly identical situation last Thanksgiving with our double-basin Kohler sink. The water woud just sit there for twenty minutes after doing the dishes, and I kept pouring Drano Max Gel down there hoping for a miracle. Like you found out, those chemicals ussually just sit on top of the clog and don't do much once the grease has solidified into that white, waxy soap-scum gunk. I ended up grabbing a 25-foot Ridgid Power Spin snake from Home Depot. I had to go about 12 feet into the wall before I felt the resistance break. It wasn't the P-trap at all; the blockage was way down the line where the kitchen pipe meets the main stack. One thing that helped me was running a bit of hot water while I was cranking the snake to help emulsify whatever was left. Just be careful with that expanding foam—I had some of that Great Stuff around my dishwasher lines and it's a nightmare to scrape off once it hardens on the PVC.

My kitchen island setup actually had a diferent culprit. I spent hours snaking the 1.5-inch PVC line and found nothing, wich was incredibly frustrating becasue the water was still backing up into the left basin of my Elkay sink. I eventually looked at the Studor Mini-Vent that was tucked way back behind the disposal unit. Those mechanical vents have a little rubber seal inside that can get stuck or perish over time. Once I unscrewed the old one and replaced it with a fresh Oatey Sure-Vent I picked up at the hardware store, the drainage improved imediately. If you’ve run a snake 15 feet out and come back clean, check the vent before you start cutting into the drywall. It’s a quick fix that often gets overlooked when everyone assumes it's just a grease clog.

I had a similar headache with my double sink last summer. Snaking didn't do a thing because the blockage was actually a piece of plastic stuck right in the center baffle of the waste tee. I had to take the whole assembly apart and poke it out with a screwdriver.

Now, every time I've got the pipes open, I check that baffle first. It catches toothpicks and plastic wrap like a magnet, and no amount of chemicals or light snaking will move it if it's wedged in there tight. Definitely pull the whole tee off if the P-trap looks clean but it's still backing up.

You guys're lucky it was just a clog. I spent a whole weekend snaking my line only to find out the house had settled and the pipe was backpitched. Water wasn't draining 'cause it was basically trying to flow uphill.

Check the slope with a level if you're still havin' trouble after snaking. If it's flat or slopin' the wrong way, no amount of snaking's gonna keep that grease from settling right back in. Doesn't matter how clean you get it if the physics don't work.

Quick update — I’m glad I checked the slope like one of you suggested. Luckily, my pitch was fine, but that point about the center baffle in the waste tee was spot on. I found a tiny bit of plastic stuck there too. Between clearing that and snaking deep into the wall, the drain is finally flying. No more expensive plumbers for me!