I agree with FireIsHot, I do not see any economical way to pump out muck as a DIY project. I am not aware of any commercial operation that does it that way - which usually means it is difficult and expensive to use that method.
The rental on a large 8" trash pump would almost certainly be more expensive than renting a mini-excavator.
If you can't dump the spoils pile in a flat place or in a dump truck, then you might be able to build a crib on site and line it with weed barrier or similar material. The water should slowly drain through your material, but you might have to move the remaining slop a year later after it dried.
I think a Gradall would be the most built-for-purpose machine. You can exactly set the slope of your pond bank by telescoping out of the excavation. (They can be rented in some locations.)
Gradall Clearing a Ditch
