My daughter and her husband have purchased a home.
It has 5 1/2 baths.
I mentioned that since they are the only occupants, they need to make sure to regularly use all the toilets and faucets, to ensure good condition of pipes.
They looked at me as though I had three heads.

Am I right?
Is there any information that discusses pipe/toilet maintenance of seldom-used water supplies?

You don't have tree heads, but perhaps you have two!

No need to worry about the condition of pipes for seldom-used fixtures. The only concern is keeping a minimum amount of water in the P-trap in drain pipes - that's the loop of drain under the sink that holds water which blocks sewer gasses from coming up into the home. If the sink is not used for a long period of time the water in the trap can evaporate, and you'll start to smell sewer odors. So it's a good idea to run some water in each sink, bath tub, and shower at least once every few months - you don't need much, just a cup or two. In addition, if you have a drain in the basement floor or laundry room floor, it's a good idea to occasionally pour a cup of water down them as well.

One thing for sure, if the water in the toilets that are unused gets low there can be odors that will filter up from the toilet. Also, if they are in an area where the systems
are given a smoke test, be ready for some nasty returns. South Carolina is famous for doing that.

I agree with Ebaines, Thanks.

John

Mparm5,
Sanitary trap seal evaporation can occur more quickly in warm climates, especially during the air conditioning season, and, homes located in cold climates can have excelerated evaporation during the heating season. Private sewage disposal systems are more likely to produce offensive odors in the event of an open trap, and, drain flys and other bugs can also find their way into a home with open drains or traps. Homes connected to a municipal sewage disposal system can have issues with mice, rats, snakes, and other creatures in the event of an open drain or trap.
I would suggest visiting each bathroom weekly, and, make sure to locate the shut - off valves for each bathroom group in the event of a water emergency...