I've had some luck w/ a trash pump and a settling tank.. if you use water to stir the material up it flows pretty well. The key is the settling tank has to be large enough. We also manufacture a type of Vac truck... that is VERY effective at removing everything from water, garnet and 'drop's from the tank.. as long as they are smaller than 4". It takes about 8 minutes to pull off 5000 gallons of water and then another hour or so to pull out the rest of the material.. If you have access to a 'hydro dig' operation where they can suck it out for you.. it'll be faster and cheaper than most everything else with zero chance of damage to the tank etc [compared to an excavator etc]. We used to pay $4-500 each time we had them in [until we started to manufacture our own]
Fwiw
JerryFlyGuy
The more I know... the more I realize I don't
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)