Term for "will consume time and almost certainly yield nothing"

Term for "will consume time and almost certainly yield nothing"

Can anyone point to an eloquent word or term that means "will consume time
and almost certainly yield nothing"?
Could be used in response to: "I'm going to have one of the developers
contact Apple and ask them to add a new feature to Apple Maps."
The effort has a tiny chance of being successful, but if you knew how the
sausage was made, you'd know that asking the question isn't even worth the
time.
At first I thought "invading Russia" might have been apt, but that kind of
implies that you're going in with a lot of firepower only to slowly lose
and retreat. It's also competitive in nature. That's more more appropriate
if someone said "I think we can take Amazon.com head on."
The only other thing that came to mind was "mining for unobtanium". I'm
open for better, though.