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We live on a windy coast of North Sea. High wind is a norm here. One of the problems I face with the wind: it comes out from kitchen sink drainage pipe. If it is blowy outside, you can feel a draft coming from the drainage pipe.

I think the problem is because the drainage pipe finishes outside and does not make a sealed connection: Drainage pipe is not sealed

Because the drainage pipe is not sealed, the wind blows up the pipes and comes out from my sink drain. Making the kitchen colder (we have enough vents there already!)

Is there anything can be done to prevent this draft?

I'm thinking cover the drain hole (the one on the picture) with something, but could it not cause more problems?

UPD: Pipes under kitchen sink look like this: enter image description here enter image description here

Thin pipe on the first photo on the left is a waste from dishwasher.

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6 Answers 6

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You don't have a trap seal, to prevent air from moving through the drain.

enter image description here

Only the dishwasher is draining through the trap, so there's no trap to prevent air from coming up the drain. you'll have to fix the plumbing, so that both the sink and dishwasher use the trap.

Instead, the plumbing should look more like this...

enter image description here

Use a tailpiece like this, off the bottom of the sink.

enter image description here

This allows you to connect the dishwasher to the drain. You can trim the end of the tailpiece, so that it fits into the space you have.

Connect one side of the trap to the end of the new tailpiece, and the other end to the drain pipe.

You'll also have to add a vent to the system. Depending on where you live, air admittance valves (AAV) can be used.

After looking more at the plumbing, you might not need additional fittings (other than for venting).

  1. Remove the sanitary tee connection from the drain.
  2. Connect the dishwasher outlet to the sanitary tee, where it used to connect to the drain.
  3. Connect the end of the trap (where the dishwasher used to connect), to the drain.

Basically, just swap these connections.

enter image description here

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  • 2
    You are a scholar! Indeed I can get away with just swapping these 2 pieces. I think the dishwasher was installed as an afterthought to the plumbing and by somebody not knowing what they are doing. I found a lot of small issues like that left by the previous owner.
    – trailmax
    May 2, 2016 at 14:55
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    Tester pretty much nails it. You also want that dishwasher drain line affixed to the underside of the counter top in at least one point to minimize the risk of water feeding back. And that's effectively an S trap, not good but fixable. Changing the 90 elbow in the back to a tee with an AAV as close to the countertop as you can get it would be the fast solution.
    – BMitch ♦
    May 2, 2016 at 15:17
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    @BMitch good suggestion about fixing the dishwasher drain to the top - it is very heavy and pulls the current installation down. See how twisted the bottom U sits comparing to the vertical pipe - it used to be vertical, but been pulled down.
    – trailmax
    May 2, 2016 at 16:20
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    The back feeding risk into the dishwasher is that a clog in the drain will backup into the dishwasher instead of into the sink. You wouldn't even know there's a clog until you open your dishwasher and find it full of your sink waste. When you affix the dishwasher drain to the underside of the countertop, the sink has to nearly overflow before anything can drain back into the dishwasher.
    – BMitch ♦
    May 2, 2016 at 18:55
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    A vent is not needed, as the pipe exits into a outside drain with a air gap. Even if the pipe was sealed into the underground pipes, a vent is often not needed provided the underground pipes are vented correct by he soil stack. (lots of examples in the UK building regs).
    – Walker
    May 3, 2016 at 10:35
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You could put a cover over the drain box but when you do so it has to allow for free air flow so the isolation afforded by that air gap drain box still functions properly. If I was making the cover it would have a baffle design with a double wall construction. See figure below:

enter image description here

The inner wall of the baffle cover would sit on the ground or maybe even set below grade. The outer shell would not come all the way down. The picture is somewhat conceptual and does not attempt to show how the two parts of the cover fasten together.

Before committing to an elaborate construction project you could prototype the design to determine how effective the concept is. This could be done using heavy corrugated cardboard carton material. You easily cut the cardboard with a sharp utility knife and a straight edge. The pieces can then be joined together with hot melt glue. (Hot melt glue sticks to the brown corrugated cardboard amazingly well). Hold your prototype in place using some bricks to keep the howling wind from blowing it away.

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  • That's pretty awesome drawing! And cardboard prototype is also a great suggestion. What material would you use to make the non-prototype?
    – trailmax
    May 2, 2016 at 11:19
  • You could use various materials I suppose. Wood would unquestionably be the easiest to work with if you have the tools for that. But sheet metal may be feasible. The most weather resistant may be to use a wood frame that uses flat fiberglass sheeting for the top and sides. (I speak of the type of fiberglass material that is often used in a roof to allow light to come through. It could be glued to the wood frame using construction adhesive.
    – Michael Karas ♦
    May 2, 2016 at 11:26
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While I agree that this was assembled backwards I think the apparent lack of a vent is acceptable here. It looks like it basically goes through the wall and then into that box outside--so long as it's close enough to the sink that would suffice for venting.

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  • That's correct - drain pipe goes through the wall and outside. And there is not much space for the vent anyway. Also I checked local DIY store (B&Q in UK) and plumbers there had no idea about vents (does not mean anything though)
    – trailmax
    May 3, 2016 at 0:20
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Most drains (in the US) vent thru a vertical pipe which prevents sewer gas from accumulating in the structure (home,apartment,etc) Part of that system should include a trap (usually a J or S shaped piece of pipe which holds a small quantity of water which prevent air or gasses from passing back into the room from the sink or toilet. If that trap was not included air ("wind") might be noticed.

Check for presense or lack of a trap.

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  • There is a S-shaped trap under the sink.
    – trailmax
    May 2, 2016 at 12:57
  • S traps are not permitted in a typical drain setup because they result in the water draining too fast and sucking water out of the trap (your local codes and gray water system may permit it). You want a J trap with a vent connected where the line goes vertical to avoid sucking water out of the trap.
    – BMitch ♦
    May 2, 2016 at 13:09
  • Possibly it is J-trap, I'm not entirely sure about the difference - it was set up by builders when kitchen was refurbished.
    – trailmax
    May 2, 2016 at 14:03
  • A properly functioning trap should have water in the bottom of it after you use the sink. I think we'd need to know if your trap never works (never fills with water), gets sucked dry when you drain a lot of water quickly, or dries out due to wind pressure over the outside pipes.
    – BMitch ♦
    May 2, 2016 at 14:09
  • @BMitch See update - added photos of how it looks under the sink. I think you might be right, the piping looks wrong. Also sometimes I get standing water on the bottom of dishwasher.
    – trailmax
    May 2, 2016 at 14:20
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All you need is a trap on both paths like the one you have coming from the dishwasher/washing machine

The trap fills with water and stops draughts although in excessively windy conditions its still possible for very strong winds to force their way through a water trap but normally there wont be enough pressure

I wouldn't personally suggest swapping the fittings over personally as theyre pretty cheap, so I would say its better to get a second trap or I bend and fit it between the sink and the outside pipe

removing it from the other pipe will make it more likely that food waste that goes down the plug hole could end up in the draining pipe from the appliance and risk causing a blockage if there isn't a filter, and even if there is a filter it could could clog the filter up

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An easy test would be to cut a panel out of some junk styrofoam, that would go under the black grate, and block up but not tightly seal, the tub that the white pipes drop into. It's free and easy to work with, and if such a block cuts down on the wind problem, you can then make something more permanent and better looking.

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  • Sounds like this is the sink drain, so it's actively used.
    – Daniel Griscom
    May 2, 2016 at 14:00
  • I mean around the pipes, not underneath (and thereby blocking the outflow).
    – Pete Danes
    May 2, 2016 at 14:02
  • Ah. You might also consider wind blowing up the external drain pipe; there's no info on where it actually goes.
    – Daniel Griscom
    May 2, 2016 at 14:04
  • Cutting a flat panel out of junk styrofoam that would sit where the black grate sits now, roughly around the pipes, but not tightly enough to seal would block wind from the entire system. Put a rock on it to keep wind from flipping it out, and see what effect it has.
    – Pete Danes
    May 2, 2016 at 14:12
  • It's unlikely, but I was wondering if wind could come up the lower drain pipe itself (e.g. if it ends pouring off some cliff somewhere). Absent that, good idea, although you might want to make the answer clearer on exactly what you're blocking.
    – Daniel Griscom
    May 2, 2016 at 15:13

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