"Understanding Your Home" by Building Inspector Mark Visser
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Gurgling sounds. Main stack. Soil stack. Vent stack
TIP - DRYED OUT DRAINS?
USE BABY OIL INSTEAD OF WATER

If you haven't used a sink, a shower, or a garage drain in a while, the water in the trap can dry out. This will allow sewer gases to enter the house. For a quick solution you can pour water down the drain but that will evaporate over time. For a more lasting effect pour baby oil down the drain.

WARNING - ABOUT SEWER GAS
If snow and/or ice prevent you from going on the roof add water to the drain where the gurgling sounds are coming from to replace the siphoned out water. A dry drain and p-trap could allow sewer gasses to enter the house. Sewer gas is bad for your health and even worse, highly flammable. The vent should be unblocked as soon as it is safe to go on the roof.


TIP
For more info on how fixtures, drains, vents and main stack are interconnected go to Vent and Waste Systems.
Gurgling Sounds when Flushing Toilet





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Gurgling sounds. Main stack. Soil stack. Vent stack.
On more than one occasion during my career as a building inspector have I heard gurgling noises when checking out plumbing fixtures. Last winter I encountered the same problem in my own home. Snow and ice prevented me from getting on the roof to check for a possible cause but by the time spring arrived the gurgling sounds were gone.

GURGLING SOUNDS. WHERE and WHEN
Not all gurgling sounds are caused by problems in the plumbing draining/venting system. It is normal to hear these sounds in the toilet at the end of every flush because of air suction into the toilet bowl.
Gurgling sounds are not normal when we flush the toilet and hear the sound coming from a nearby vanity sink or bathtub drain.
If you hear the sounds only in the winter it is most likely caused by freeze-up of condensation in the main stack above the roof line.

WHAT IS CAUSING THE GURGLING SOUND?
Drains from all plumbing fixtures are connected to a vent. Each fixture has its own vent. In turn, all vents are connected (usually in the attic) to the main or soil stack which allows air to enter the plumbing system.
When a toilet is flushed the falling water creates a suction and air is pulled in through the vent stack on the roof to relieve the suction. When a vent becomes blocked it prevents air from entering the plumbing system. Then, when a toilet is flushed, air and water are sucked in through the nearest trap (often the tub drain) and you will hear gurgling sounds.

POSSIBLE REASONS FOR A CLOGGED VENT STACK
Gurgling sounds are almost always associated with venting problems due to a clogged or partial clogged main stack. The main stack is that short section of plumbing pipe above the roof line. This vent stack is not covered and open to the atmosphere. Depending on local plumbing codes the diameter of the stack is 3-4 inches (75-100 mm). Older soil stacks were made of cast iron while PVC or ABS is used for all new installations.
The soil stack can become clogged for many reasons:
- Birds making a nest inside the stack or squirrels stuffing down leaves and acorns.
- Frozen spider webs trapping debris.
- Main stack is covered by snow.
- Main stack section above the roof line is too long.

WARNING ABOUT GOING ON THE ROOF
Do not access and walk on roofs if the pitch (slope) is more than 4-12. Wear running shoes or work boots with a high tread profile to prevent sliding and slipping. For steeper roofs call a professional to check out and clear the vent stack.





HOW TO REMOVE THE BLOCKAGE AND PREVENT IT FROM HAPPENING AGAIN
Obstruction near the top
When it is safe to do so go on the roof with a garden hose. Check the vent stack. If it is clogged remove all visible nesting material and other debris. Use the garden hose to flush down any loose material.
Obstruction further down the soil stack
Lower the hose and poke at the blockage. Turn on the water. After the plug breaks the hose will move freely. If you are unable to break up the blockage you may need to rent a plumbers snake or call a plumber.
Snow
Deep snow can also block the vent stack. In most cases the warm air will melt the snow that has buried the soil stack. If there is too much snow you may have to go on the roof to clear the vent opening. Only go on the roof if it is save to do so. If snow blockage is an annual problem you may have to install a de-icing or heater cable.
Vent freeze up
The length of the vent stack should be no more than 12" (300 mm) above the roof. If it is too long there is the potential for complete frost closure. Warm air inside the vent will condense and freeze before it can be expelled outside. In severe weather conditions the vent will freeze up completely. The system is than unable to draw in air for venting and you will hear gurgling sounds.
Temporary solution: Pour boiling water down the vent pipe.
Long term solutions: - Cut long vent pipes down to 10-12 inches above the roof line. - Make sure to insulate or re-insulate the section of vent stack going through the attic.


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