It obvious by the looks of him that Ronald never bathed since his house was put up for sale and when the new occupants moved in. Shouldn't his body odor have caught their attention at some point? The longer he didn't shower, the further his stench should have traveled.
In the book the family did begin to notice an odor, although that may have had something to do with bodies buried in the crawlspace under the house. Ronald is a much darker character in print.
He had a toilet and flushed it only when he heard another toilet elsewhere in the house.
This is one of the very few IMDB credits for the late, great Jack Vance. It's from one of his lesser books and not very characteristic of his work. The bulk of his writing was in science fiction and fantasy, and he was one of the great stylists of the genre.
I was just wondering about the toilet flushing and sink noises, but what you said helps explain it. I guess no one would have noticed mysterious water and plumbing sounds if he would only use the toilet/sink at the same time as someone else.
The book sounds really interesting. It's extremely hard to find in print (at least at a decent price), but I noticed that it is now available to download as an eBook. So, that's good! I might check it out sometime.