My 10-year-old gas furnace has a small drain pipe to carry away condensation, which I plumbed into the house system using an arrangement whereby the drain drips into an open trap. On average the furnace puts out almost a quart of water per day. Recently there was some strange seepage on the floor around the false cabinet where I had enclosed the drip drain. When I removed the top of the cabinet and took a look I found that the trap, an ordinary 2-inch black PVC p-trap, was in two pieces with a jagged break, as if if it had been hit by a giant hammer. So the furnace drain was just dripping on the floor. What could have made a piece of PVC break like that? - It didn't freeze; it is well inside the house, and our heating system has never failed. - There's no stress on the trap itself, nothing even touching it except the outgoing pipe it is glued to. - The space it's in has been nailed shut for 10 years (and no, there are no nails anywhere near it). - We've never had rats or any other pests, not even so much as a cockroach. Groping into the realm of the bizarre for an explanation, could the furnace condensate contain tiny amounts of burn products from the natural gas, which very slowly corroded the PVC? I know that's probably ridiculous but I'm completely mystified.