Barnprincess81 also wisely mentioned watching out for fry in the "out" container. Sooner or later that happens to all of us.

Someone with more sense than I, suggested using a light (white?) colored out bucket to dump water from tanks. That way one can see fry and other accidental refugees.

Now my out buckets are black (and sometimes used for other noxious tasks). The in buckets (also used for washing new and boiled gravel) are white and yellow. But I will use one for the fry areas, If it is dead baby brine shrimp I am removing, the empty bucket will sometimes be left in the sun or bleached and dechlorinated, because that gunk in fry tanks can be bacteria and parasite rich.

Miskairal's and NGM's response to your other question, made me think about your other question. A lot of creatures have the birthing canal near the intestinal outlet. Even humans close to giving birth, will often have to consult with a toilet.
I guess birthing, for many creatures, can be a pretty messy process.

A fry may also get briefly entangled if the mother guppy is "constipated". Constipation (unlike the definition some college mates gave of where a guppy swims up to a plant, grabs hold with the pectoral fins and strains a lot) is where feces hang or trail from the guppy. Maybe increasing the content of brine shrimp or Daphnia (with their shells) or of vegetable bulk with veggie flakes or the crushed insides of cooked peas, will help break those strings up and facilitate the elimination process for guppies.

Yours was an unusual question. But is very legitimate.

It is always interesting to get a question which both is brand-new to Guppylog and a bit of a "stumper". You certainly had me pondering that while running errands and attending a meeting last night. Thanks!

And without M's and B's suggestions above, I never would have hit on anything.