Dear Matthew Alice: This morning I heard a rumbling sound in my unoccupied bathroom and went there to find that the noise emanated from the toilet bowl. The water in the bowl was trembling, the noise got louder, then the water went down the drain making a sort of loud gidping noise. Is there a really big dog in my pipes or what? — A. Genie, faxland
Random unmanned toilet flushing isn’t unheard of, but it’s not related to wildlife in the plumbing. Your toilet is just the feature item linking two hydrodynamic systems. The incoming end works on water pressure, the outgoing mostly on gravity. We checked with experts in both ends, and all said they’d need details about your particular toilet and sewer system to answer positively. I already know more about your toilet than I care to, so they had to work with what you gave them. There’s a long-shot chance that some clog in your sewer pipes broke loose and caused the water in the bowl to back up, then drop enough to cause the pipes to shake and the toilet to flush. But when pressed, most opined that you had a surge in the water pipes that feed the toilet tank. The rumbles and jiggles came from the increased pressure and vibration in the pipes, which might also have caused the flush valve to open, especially if it was already a little leaky. Less mysterious and interesting than you’d hoped, I’m sure.