Your home's supply and drainage system must always be two distinct subsystems, with no overlapping. At the fixtures (bridges between the two systems), the air admitted by the vent stack and vent pipes keeps the traps sealed and prevents sewer gases from backing up through the drains. See more plumbing pictures.
fix common leaks from a temperature and pressure relief valve or a water heater drain valve by checking temperature settings and mineral deposits. a simple cap solves the water heater drain valve problem.