After much help from the other answers here, I have finally come to the end of this rather distasteful puzzle—yes, I know it is in aid of charity, and am surprised at my own distaste—and have had my fill of lavatorial puns, but this one shortie remains.
Thanks to both. Since I am late completing this, today is SUN, though I downloaded it on FRI. Anyway, never thought of SAT. I rather thought that "puzzle's point" might be thematic—but enough of that already! RB.