Why is my kitchen sink still draining slow after I redid the venting?

Nine times out of ten, when an AAV setup is still backing up after a clean snake, the issue is the elevation of the vent or a lack of pitch on the horizontal arm. If your Studor vent is sitting too low, it won't break the vacuum effectively. Most codes and manufacturers require that valve to be at least 4 inches above the top of the **trap weir**. If it's tucked right behind the sink bowl or level with the drain arm, it can't breathe. Pull the vent off entirely and see if the sink drains; if it clears out immediatly, you've got a faulty valve or it's just positioned too low to do its job.

But don't overlook the slope on that new horizontal run you built. Since you converted from two drains to one, you might have created a 'belly' in the pipe or lost your **1/4 inch per foot** downward slope to the wall. Water won't move if the pipe is level, even if the line is clear. If that arm is flat, the water just sits there and creates its own air lock against the incoming flow from the basins. Check it with a level to make sure it's actualy heading downhill toward the wall stub. Another thing to check is that disposal connection. If it drains fine when the disposal is running but sits still when it's off, you're likely looking at a grease buildup or a partial obstruction right where the disposal discharge meets the tee. Even a small amount of sludge there acts like a dam. Since you allready snaked the wall, the problem is almost certainly in the way the new baffle tee and trap arm are sitting under the cabinet.

Try the 'no-vent' test first by unscrewing the Studor. If it's still slow, you need to adjust the height of your wall connection or shorten the tailpiece to get more drop. It sounds like you've got the right idea with the single trap, but kitchen sinks are fickle about physics when you start adding air admittance valves into the mix.

When you snaked it, did you actualy feel it drop down the vertical? I’ve seen plenty of folks run a cable trough a wall tee only for it to head straight up the vent pipe. If your snake came back dry, you didn't even hit the clog. Back before we had these plastic AAVs, we’d have to cut into the cast iron to see the real mess.

Check if there's an old 'sanitary cross' in the wall where those two lines met. Those fittings let water from one side jump right over into the other instead of going down. That kind of turbulence will stop a drain cold.

Have you ruled out the baffle tee itself? I’ve seen those new 'all-in-one' kits have a plastic burr or a misaligned divider right where the disposal side meets the main tailpiece. If that baffle is blocking half the flow, it doesn’t matter how clear your wall pipe is. Also, you mentioned it's a double bowl—did you check if the sink's basket strainers are actualy seating properly? Sometimes the simplest mechanical blockages in the strainer itself look like a venting issue when they're really just not letting water into the pipe fast enought.

Check the height of your wall stub-out against the discharge on that InSinkErator. If you upgraded to a deep 9 or 10-inch sink, your wall drain might acutally be too high now. I’ve seen guys install a fancy Badger 5 only to realize the outlet is sitting lower than the pipe in the wall. If that’s the case, you’ve created a permanent 'belly' that no Studor 20341 can vent out of. You need at least a 2-inch drop from the disposal outlet to the wall penetration to keep things moving. Grab a tape measure and see if you're fighting gravity before you tear more of that PVC apart.

Spot on about that wall stub height. I've seen that exact 'too high' wall drain issue trap air in the top of the pipe, effectively making a second trap. One detail people miss when they swap to a single trap is the baffle tee orientation. If you installed a directional baffle tee upside down or if it's a 'T' instead of a 'TY' fitting, the disposal water will actualy shoot straight across and hit the opposite wall of the pipe, causing a splash-back turbulence that stops the drainage cold. Check that the internal diverter is actually pointing the water down toward the trap.