I still don't exactly understand the men in the tiny kitchen

Once The National moved into its permanent headquarters, a lovely, sprawling room shored up by royal blue pillars and decorated in all white, I noticed a man in the tiny kitchen where the kettle sits. There is a much larger, more modern kitchen around the corner. Oddly, it does not have a sink or a kettle.

But back to the tiny kitchen and the man inside. He wears a yellow vest and a white shirt and looks quite smart. He has a bushy black moustache. After a couple of days, I realized he runs the little kitchen. Mostly, his job seems to be keeping the kettle full of piping hot water for tea. I have been so gobsmacked by this feature of my new job, I failed to notice when there were not one but two kettles and, before long, not one but two men manning the kettles. And quite often, one of them actually serves some of my colleagues tea and/or coffee, right at their desks.

Also, they wash our mugs. I know this because my treasured "What's the news?" mug disappeared one day. Then, the next day, it was back on my desk. A couple of days later, it felt as though I had just taken my last swig of tea when I looked at the place where it had been, and it was gone. When I looked back at that spot again, about four minutes later: clean mug. I never even saw the hand that took it away. These guys are good. Not to mention stealthy.

I was speaking with some of my co-workers about this (the ones who are served tea at their desks) and they inform me I should be giving these men money because they are expats and probably aren't making much at all. Also, that is how they've been getting served tea at their desks. Now I just don't know how to give the men money. It feels so awkward. When I pop in to get some tea, should I just lay down some bills? Should I make a big production of it?