@Yvonne774
For short term renters I don't say anything about over usage. It isn't too often. Just like you say. I also live near a beach and they often put towels in there full of fine sand that can't be good for it.
I have put labels on the machines.
"Don't overload. Half full max"
As overloading them can shorten the life of them. Some will cram bed spread, towels, sheets, into one load.
"Open Here" on the side of the door to pull on or they will pull on the wrong side, and pull the door off the hinges.
"Clean lint screen after every use"
So you could put a note on the doors with a message. Its worked for me, no one complains, and 99% follow the instructions.
I would add more about the sand, but at this rate, think they should last a normal life span of about 10 years.
Other host will say this is excessive and off putting, but the cost of replacing one door would be over half the cost of a new machine, so it's the only way I can provide them, and if guest break them I would need to refund the next guest, it can take 2 weeks to replace, etc.
The drain should be connected to the sewer line, so I wouldn't try and make a claim or issue if it drains back under the house.
If it becomes too much trouble consider taking them out, although I would try the notes on the door first. "Please try to limit use to one load per day. Thank you" Put that in you listing as well.
I can hear the pipes banging. It is annoying when guest like you mention run them non stop. That's one of the reasons I went from 4 guest to 2 guest. Some, I guess, would load up their mini van with all their blankets from home, as they would run them non stop, and some just obsessed about doing laundry all the time, because they think it's free. Not very considerate.