Occasional Odor From Bathroom Sink

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k75s57

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• Occasional odor coming from MBR sink. Not repeatable on demand.
• All sinks, toilets, shower, tubs drain easily. No gurgling or bubbling.
• Using a bright flashlight on the sink trap and looking down the sink trap I see the following:
• trap always has water.
• trap water line has slight bounce when toilet flushes.
• trap water has slight bounce on winding days.​

See attached diagram.

With the odor not consitent want to try to determine a better cause before contacting a plumber.
 

Reach4

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You have a sink in your master boot record? :rolleyes: OK... I figured out what you meant.

How about a better photo of your upper left photo?
 

Sylvan

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EASY FIX get Clorox or Hydrogen peroxide and pour some down the OVERFLOW of the sink same for the Tub as bacteria builds up and can cause periodic foul smells
 

k75s57

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Additiona Info.
-Additional attachment provided.
-No odor if sink drain is closed with water in sink.
-More details for original diagram regarding top left photo.

I did see some stuff coming out where sink overflow connects to sink drain when pouring water in overflow hole.

Original Info.
•Occasional odor coming from master bedroom bath sink. Not repeatable on demand.
•All sinks, toilets, shower, tubs drain easily. No gurgling or bubbling.
•Using a bright flashlight on the sink trap and looking down the sink trap I see the following:
•trap always has water.
•trap water line has slight bounce when toilet flushes.
•trap water has slight bounce on winding days.

I was using MBR as master bedroom. I modified diagram to be more clear.
 

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  • Sink P Trap.jpg
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  • Venting.pdf
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Reach4

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What is going on here?
img_3.png


No odor if sink drain is closed with water in sink.
That is useful troubleshooting information. Sometimes it is hard to identify the source of a smell.

EDIT: I wonder if somehow the trap is siphoning for some odd reason. Does that sink drain really fast when you open the stopper? That long drop to the trap could help get things going fast.
  1. How about letting out a basin of water suddenly as a test. Is the level of the water that you see in the trap lower after that?
  2. After using the sink, follow up with some water flow into the sink at a low rate to refill the trap after any potential siphoning.
 
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k75s57

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In the picture it shows an attic venting connection with some attempted added markings to help show what is happening.

-Top connection is an immediate 90 degree downward which pickups 2nd floor hall bath immediately below this connection and that same line continue down to the basement.
-Left side is horizontal venting going to master bathroom sink/toilet. Where I get the occasional sink smell.
-Right side venting is continuation of venting going to roof vent stack and it picks up another 1st floor powder room with a T along the way.

Sink trap stays intact no matter on the speed of the sink drain
 

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WorthFlorida

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When the wind blows or a toilet is flushed, water moving in another toilet is the air pressure in the vent system drops (negative) allowing the higher pressure inside the home to push down on the water. For the MBR sink the trap, as suggested above, is slightly being siphoned and lowering the water level in the trap.

If this is something new, you’ll need to check the vent at the roof. You have a 3” pipe through the roof line to minimize it from frosting over. At the elbow it looks like a 2” to 3” union at the elbow. Possible a squirrel or bird fell in from the roof opening partially blocking the ventilation. A test is run a garden hose down the vent pipe from the roof. It should drain quite fast and any backing up indicates blockage. All vent pipe must slope toward the main stack. With all your horizontal pipes it is possible that water is laying in the pipe partially blocking air flow. That picture shows too many connection at one point and it also could be restricting proper air flow or holding water. Rain water does enter the at the roof vent.

A solution at the sink is add an AAV. It should provide enough air to prevent any siphoning of the trap and reduce negative air pressure. This video shows a problem with a non vented system but a partially blocked or not enough vent would be similar. I know you don’t hear gurgling.

 

k75s57

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All thanks for the assistance. I just added a new sink and trap in Dec '19 so the random smell has not been occurring very long.

Solved the problem with a gallon hydrogen pre-oxide and test tub brush. I focused on getting gunk out of where the overflow part of the new porclain sink ties back to the drain connection below the sink and I scrubbed the drain pipe down to the p trap.

Thanks Sylan.
 
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