I don't have any bottom drains in my lily ponds & the last couple of inches is always a big mess to clean up. Scooping muck with a cup into buckets, shop vac which gets way to heavy to empty plus the clean up of it afterwards, & the last bit of filthy water that needs sucked out.
Finally remembered to buy a boat bilge hand pump & it really does help suck out the last bit of water. Still have to scoop muck but at least it is more solid. Plus after hosing the pond down of the last bit of dirt before filling, the hand pump made is much faster to clean up that last bit of dirty water. Just wish the hose on it was about a foot longer.