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Then I think that it’s a very reasonable request.
If you can improve the facilities you offer to your guests, then that’s a good thing. As long as it’s not an expensive alteration - but be sure to allow for the extra facility when you’re working out your nightly rate. 
Yes, I understand how they work. I was simply saying that I find it somewhat discomfiting. I don’t really want the place where I wash my face and teeth to be that close to the toilet bowl. I’m not much of a germophobe, it must just be the optics of it. But I’m completely cognizant that the idea of people using clean drinking water to flush toilets is incredibly wasteful.
Really? Like the one next to the toilet? And the kitchen sink? I seriously doubt it. I mean really, the toilet is right there…
I pee outside, I pee in the shower I pee freely wherever I needly but never a sink when a toilet is freely!
RR
Yes, really. Men pee in sinks. Even when the toilet is right there.
You must have some real pigs in your circles, and coming from me that’s a lot. I will pee almost anywhere but not in a sink next to a toilet. How do you know this to be true? Scroll up this thread and I see where a woman sat on a sink and knocked it off the wall though.
RR
My husband cleaned bathrooms for seven years at an airport—bathrooms where he never saw men waiting in line. Men definitely pee in sinks.
Men don’t wait in line because its a mans world and there are more toilets available. I have never once ever ever ever seen anyone pee in a public restroom sink and I have been using public mens rooms for 50 plus years.
Sorry but I call bullshit, your husband hated his job and made stuff up. Not to say it has not happened, it just has to be super rare.
RR
He really did love his job. He did all kinds of airport maintenance for the seven years he worked there (his college and grad school years). He was part of the fire-fighting team, he repaired light fixtures, he cleaned offices, he washed windows, he vacuumed acres of carpeting, and a lot more. He and his team took a lot of pride in their jobs.
His favorite job was when the tower called with a task. He and a co-worker drove out on the runway with the windows rolled down, both of them screaming out the windows, to scare away birds. He had a blast and made lasting friends there.
Yes, he saw plenty of evidence that men peed in sinks. He also says, contrary to what many would think, that the women’s restrooms were much dirtier much faster than the men’s were.
Since our standard of evidence is so low, I offer this:
A simple google search offers plentiful anecdotal evidence that men do pee in sinks even if there are nearby toilets.
I wonder if they ever pee in kettles?
I hope not, I still do not believe it is widespread, I have seen a lot of stuff in mens rooms but never anyone peeing in a sink.
I will consider myself schooled , I guess I am wrong.
RR
When I was growing up, before my step-dad became a teacher, he was a janitor for many years. His brother, my uncle, who also lived with us for a few years, worked with him as a janitor. I often went with them to do “rounds” and helped a bit. We were a janitor-household for awhile and I completely concur with @RebeccaF.
Also, women are the worst about not-flushing.
Worth noting, I suppose. My husband and I have noticed that bathroom sinks in newer US hotels are now quite high and have a setback of inches from the edge of the counter. So high and so set back that it would probably be difficult for men to pee in them.
Also so high that a person of my height (5’4”) has a bit of trouble brushing my teeth at such a sink. Makes me wonder how children brush their teeth there.
Anyway, using the extra-high and set-back rule might discourage sink-peeing. By all those but the most intrepid, I assume.
Or make it messier and more evident.
Maybe they are trying to discourage people with children from booking. But a step stool like many kids have at home would be one way. Maybe kids could brush their teeth in the tub … or the toilet! 
OMG, yes, they will pee in it.
I actually use that word when discussing my time in the WC. Or when saying to friends “I’ll meet you after I perform my ablutions.” The downfall of an extensive vocabulary is that I often provide my friends with much mirth when I use those words.
Sounds like we have more than one thing in common Sailing Lady.
Hahahaha … that would normally have ignited a flame war (do we still use that expression?). Well done RebeccaF for letting that one go through to the keeper haha.
Maybe I will need to install the following sign over the basin:
“This basin is fitted with a pH sensor. Any flows with a pH less than 6 will trigger the household URINE ALERT”.
… or more challenging.