A used washer can make the pipes burst, bulge, freeze, or become detached. And it’s your responsibility to see that any of these situations are fixed when you get in touch with an experienced plumber out there.
Make sure that you ask the renters to notify you if they see any leaking or moist areas underneath pipes, since this would indicate that the connections between the pipes have been disconnected. If left unattended for too long, even small leaks might result in serious harm.
Ask your renters to help prevent the freezing of pipes during the colder months as well. For instance, when the outside temperature drops below 32°F, you need to make sure that the thermostat is left at a minimum of around 54 degrees, so that water would drip out from the taps.