This dual kitchen sink is causing a bunch of problems, mainly clogging up at the S bend.

I am a complete noob when it comes to plumbing, have never plumbed anything before and have no knowledge about pathing pipes etc. I hope someone can suggest a better path or an easy-ish fix to get better flow and not have the thing clog every 6 months.

The distance of the long dark gray pipe is around 50cm (~20in). Due to how far the outlet (?) is I'm guessing that's why the S bend (?) is all the way at the back so that it's easier to fit stuff underneath the sink. Is it possible to re-plumb the S bend and have it less prone to clogging, or does the entire path need to be redone?

Previously this sink had a garbage disposal system that eventually died and was converted to just be a dual sink. The left side apparently has missing hardware that prevents it from being connected to the sink itself, but that's a problem for a later time..

As I have no institutional knowledge, if you suggest something please provide a link to parts or a drawing so I have a visual reference, I really have no idea what I'm doing. With COVID still rampant getting a plumber to fix something this "trivial" is almost impossible from calling a dozen or so plumbers :(

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    In the vast majority of locations, that "S-Bend" is strictly prohibited - P-traps have been code minimum for decades. There are some special conditions if permitted by your LAHJ, but those require a size increase in the downward part of the drain that is notably not the case here. – Ecnerwal May 24 at 17:45
  • This was plumbed 20 years ago iirc. I'm looking at images of "P traps" but I don't understand how that would be plumbed in here? – Matt May 24 at 17:49
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    It would involve either a vent pipe you don't have, or an air admittance valve as high as possible under the sink if a vent pipe is not possible, and changing the "S-Bend" for a "P-trap" with a minimum of 2 pipe diameters between the exit of the P and a Sanitary Tee (typically) connecting to the vertical drain and vent. – Ecnerwal May 24 at 17:54
  • Thank you for your suggestion, I only wish I understood the terminology here.. – Matt May 24 at 17:55

You should be able to move the trap to directly under and between the sinks. In place of the tee going into the horizontal grey pipe install a tee that goes straight down and attach your P trap. Then run your grey pipe horizontally (1/4" per foot slope required) into the top of the drain with a 90 degree elbow.
I don't believe there are any code issues with connecting to the drain with a 90 degree elbow but if so one of the pros here will catch it.
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  • Am I understanding this correctly? i.imgur.com/xlHHSiK.png – Matt May 24 at 18:19
  • Yes. That gets rid of the S trap. However, I would replace the tee instead of rotating it. The reason is the tee in the pic has a sealed stub that rotating it will position it to catch residue and may cause you further blockage issues. – HoneyDo May 24 at 21:49
  • Thanks! Is there a way to keep the trap further down though? Having the trap there will cause some clearance limitations for bins and what not. – Matt May 24 at 22:13
  • Without vent (pipe out to the outside air, or "mechanical" / AAV), that's just a longer S-trap if you simply connect a 90 at the far end. Likely an improvement over the short S in practical terms, but not up to code in most locations. At minimum swap the 90 into the drain pipe for a Tee with an AAV on the top of the Tee, as far up under the counter as it will go. – Ecnerwal May 25 at 1:24
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    @Ecnerwal good suggestion about teeing in an AAV. Matt - If I understand Ecnerwal correctly he's saying you can move the P trap toward the back of the cabinet as long as (a) you install a vertical tee at the back of the cabinet emptying into the drain with an AAV on the top of the tee extending up as high as possible and (b) you have a minimum of two pipe widths (3 inches) between the exit of the P trap and the tee. – HoneyDo May 25 at 2:19

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