So I was about to go out and start digging tree holes, but then I got tired just thinking about it.

Lazy-brain kicked in and I realized that I should try digging it with a pressure washer.

Now my 120v washer isn't going to cut it so I'll need to buy a $400 gas washer, but I think I can do the whole job with that and either a similarly cost 2" gas pump (for sludge waste) or with a venturi-based attachment for the pressure washer itself.

Laziness promotes the best, smartest engineering.