Air Admittance Valves

I recently had to unblock a sink waste pipe.

When I was called out the customer explained that under the sink had been leaking. After clearing the blockage with my drain auger, I checked to see where the leak was coming from. That’s when I saw the plunger. Whilst it’s a good idea to try plunging the blockage, if the trap has air admittance valves (AAV) the plunger will push open the diaphragm on the AAV and force water out of the valve. This doesn’t allow the plunger to do what it is designed to do and will not unblock the waste pipe. AAVs allow air in and not out. They are designed so that you do not lose the trap seal and the diaphragm prevents water escaping from the trap. Fortunately no damage had been done to the AAVs and there wasn’t a leak.

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