Perhaps via reference to https://en.wikipedia.org/wiki/BlooP_and_FlooP ?
EDIT: though, in that context, I would parse "out-floop" as a transitive verb meaning "to FlooP more, to a greater extent, or faster, than <something else>", rendering its opposite actually "under-floop".
Btw i love "out-floop" and I'm going to try to find applications for it.