The modern washing machine requires proper installation and understanding
It started a few years ago. First there were a few inquiries. Then they increased. Now it is a regular occurrence. All of the questions (and failures) have related to the same thing - the washing machine.
The first questions that surfaced were about washing machines that discharge to a standpipe with an air admittance valve for the vent terminal. The callers all cursed out the air admittance valves, saying that the manufacturers should have known that the valve wouldn't work on washing machine standpipes.