What would be the reason for a strong odour in a rear stockroom of a retail store?
I've checked the toilet and it flushs quickly. I checked the drain in the sink and it works well. When I flush the toilet I can hear it working at the floor drain located 7 feet from the toilet. It is NOT backing up? The store sells cosmetics so the sink is used to wash cosmetics off brushes? Could they be building up in the drain? We've had 60 days of extreme cold weather below freezing. Could the stack vent be frozen over be the cause?