A build-up of dirt in the sink could be to blame for your persistent cough, cold and even ear infection. Biofilm (a group of cells that stick together on some surface) can come out full of bacteria.
Sulfates from shampoo, silicone from shower gel, conditioner and other bath products can mix with dirt and toothpaste and create a clog. The best way to avoid biofilm formation is to clean the sink manually. Use baking soda to scrub mineral deposits, use dental floss to clean under faucets, remove the faucet filter and soak it in bleach.