Why is my sink draining slowly?

Question

The sink in my kitchen drains very slowly. If the dishwasher is running, the waste water from the dishwasher flows into the kitchen sink. Eventually it will drain but it takes a while. I cleaned the plumbing, there is no issue there. I believe the issue is that the exit hole for the waste water is too high in the wall and there is no real downward flow after the sink trap.

The riffled hose that goes into the wall should have a downward slope to get a good water flow. In my case it is essentially level. How can I fix that?

The height of the hole in the wall is fixed. I don't want to increase the height of the kitchen counter that has the sink in it because my wife is only 5 feet tall and it should be at a convenient height for her to work on it. I could replace the sink with a different sink with less depth but that would also be less nice. I already switched the plumbing for a set where the exit of the trap is high relatively to the input (the limit is the entry for the dishwasher from the grey hose coming in from the back).

What else can I do to get my sink to drain properly?

A little more background and results. When I wrote 'I cleaned the plumbing' I meant the parts from the sink until it disappears in the wall. I disassembled these parts and cleaned them, there is no clogging issue there.

However, as suggested in some answers, the issue is clogging further down the pipes. The pipe in the hole in the wall has a 90° turn after a few centimeters and goes directly downwards. Poking in there with a wire it seems to go down maybe 20 centimeters or so and that is the spot where a lot of gunk accumulated. I'm in a multi floor apartment building so the building main waste water pipe will be much thicker but aparently my pipe has another bend there before it drains in the main pipe.

I poured some pipe cleaner directly into the whole in the wall and that seems to have fixed the issue. Drainage is much better and faster now. I haven't run the dishwasher yet but I hope this issue is solved as well.

Answer 1

You have a clog.

Low slope wouldn't cause this unless the kitchen is in the basement. The sewer main is well below the kitchen sink, there is no reason water would back up several inches into the sink if there was anywhere for it to flow - an ice cube melting on a perfectly flat floor still finds the lowest point and turns into puddle.

A blocked vent wouldn't cause this either, as a vent is there to slow down the flow of water through your plumbing to avoid the p-trap being siphoned. A drain with no vent actually drains faster than one with a vent, as water gets "pulled" down the drain by the accelerating slug of water.

Something is physically blocking the pipe. With water backed up into the sink, you have a hydraulic head of over a foot, meaning the water is pushing into the pipe with about half a pound per square inch of pressure or more - something is pushing back. If you already snaked the plumbing, it's possible you punched a small hole through a clog which mostly sealed back up.

Answer 2

I cleaned the plumbing, there is no issue there.

so you cleaned the plumbing starting at the wall there in the pic all the way out to the sewer, or to your septic tank?

I believe the issue is that the exit hole for the waste water is too high

academic exercise - take everything you see in that pic, put it outside in the driveway, where the drain pipe/hose enters the wall that just empties unobstructed onto the ground. Would you be able to flood the sink with too much water that it would back in the sink and drain slowly as you describe.

The sink in my kitchen

it's all the waste dumped down the kitchen sink over time blocking the drain pipe somewhere after it enters the wall. If you have any kind of horizontal run of that drain down in the basement, it may not be pitched properly and then you may find it is 90% + blocked with goo. If that 1-1/2" white drain pipe in the pic is clean, that is not the problem. Running flow-easy might eat out the blockage and fix it. Watch a flow-easy youtube demo before you buy it, be forewarned don't underestimate handling it.

and if a short 90° elbow as opposed to a long sweep 90 is used on the drain piping down below, especially before any significant horizontal run, that will be a significant cause of poor drainage to eventually happen.

Answer 3

The flex pipe is probably the main issue. It creates quite a resistance to smooth flow. I'd replace it with rigid pipe. You have a very standard situation here, so that shouldn't be difficult. By my eye, there's enough slope between the trap and the wall hub to induce good flow.

Have a look at photos of typical traps and grab some parts from the hardware store. I think you just need some straight pipe with compression fittings (like on your trap) and maybe one elbow to bend horizontally as you approach the wall hub.

Also look into how your dishwasher drain hose should be routed. They typically should have a loop well above the drain connection to prevent backflow from the sink and siphoning. That's not related to your drain issue, but it's best practice.

Answer 4

In a word: Most likely you have a clog further down the line.

Part of your problem might be limited access to the local language and/or culture (I guess you wouldn't ask here if it weren't so). That's why I give you a few locale-specific hints being at the edge of the scope of this site.

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What can you do?

(-1) Avoid the problem in advance. Do not throw waste into the sink (as seems to be common in other cultures where they have things like garbage disposal units, quite unknown in your place); pour less oil/grease/... e.g. from frying pans, and use a bit more water. And: Maybe use a protecting sieve.

(0) The trap (all the white piping in your image) is mounted as it should be (and the horizontal "riffled hose" is OK). There is no need to change this (other than clean thoroughly).

(1) I understand you do have already disassembled and cleaned the trap. (This part is underestimated sometimes). If you want to be 110% sure (or if you want to demonstrate that you have done your part, see below) you can easily replace the whole thing by an identical one, it should be less than 20 € at your local Baumarkt (e.g. here, no affiliation on my side). Official product name is "Siphon" (with french prononciation!) "für die Küchenspüle"; colloquially also known as "(der) Traps" (or "(Küchen)Abfluss" if they still do not understand).

(2) Chemical method. Pour something into your drain, and add water. This may reach a bit further into the pipe; easy to apply but I wouldn't expect too much from it.

As you seem to prefer gute & günstige Edeka products, you might try something like this (again, no affiliation).

(3) Mechanical method. Using a spiral you can reach a few metres into the pipe and clean it out. I did this a few times with partial success; yet this is quite a dirty job that may not be fun for everyone (and might better be done by a professional).

(4) Report the problem to your landlord. Where you live (I see that your question is tagged "Tagesspiegel") this (i.e. the part after the pipe has entered the wall) is clearly their responsability. (You may want to present them a fresh trap, see above.) They may not want to help immediately. Be very friendly, but tell them clearly that you want them to act before there is unwanted damage to their property due to water leaking onto the floor (and possibly into the apartments below).