Plumbing traps are curved sections of drain pipe found immediately underneath sink, shower, and bathtub drains. They retain small amounts of waste water in their curved sections so that foul-smelling sewer gases don’t waft into the cottage. These traps are either shaped like a horizontal S or P, but both do the same job.
There are two reasons why a drain trap might smell like rotten eggs: dry traps or microbial growth. In heated cottages, water can evaporate in unused traps over winter, allowing sewer gases to enter your place. If your heated cottage smells sewagey only when you arrive in the spring, dry traps are probably the cause. (In unheated cottages, traps need to either be drained in the fall or filled with plumbing antifreeze to prevent freezing and damage.)
Even properly functioning, water-filled traps can smell if they become infected with microbes. Hydrogen peroxide is an economical and non-toxic fix. Pour one cup down the drain at night, and the smell will be gone in the morning. If your sink has an overflow port, take the extra step to stuff a rag down the drain to block the entry point where the overflow port meets the drain. (It’s a couple of inches down from the drain opening.) Fill the overflow port with hydrogen peroxide after you’ve treated the trap, and let the treatment sit overnight to disinfect.
Do your sink traps have a drain port on the bottom so you can empty the water in the fall? These can sometimes drip water even when they’re tightened. Apply pipe-sealing compound or Teflon tape on the threads of the outlet to seal drippy trap drain ports.
In a pinch? Fish out an item dropped down the sink via the drain port.