Royal holloway accommodation- foundersWatch
I think the room is picked for you at random, so there's no way to know for sure if you will get a basin. I lived in founders for my second/third years where my second year room had a basin whereas my third year one didn't, but from experience having a basin is more like for first or second years than older students..
Not OP, but do you know if the larger rooms have basins? Or just the single ones? Because the website says they don't, but the accommodation brochure says they do, so I'm slightly confused.