It’s one of those “jokes” that makes sense only in print: “Lava” meaning molten rock is pronounced “lah-vah”, but I doubt that anyone pronounces “lavatory” as “lah-vah-tory”, even in Tanzania. I could be wrong.
It appears that the cartoonist is creatively spent after rendering the lush jungle landscape in Sunday’s strip: a Google Image Search for “Kilimanjaro lava tower” turns up images of an impressive, massive monolith. As drawn here it resembles a small slag heap.
Son of Stuck Funky 