post 8 by lumberjack describes exactly how we did a very similar job 'cept we used the backhoe to start the excavation, then the mini went in and threw it on the bench, every once in while the hoe TLB) would clear the bench...aside from the usual things like keeping the dig to intended size and not allowing excessive taper (eg it gets too small too soon)....I think it took us one good long day, the next day we put in the required gravel bed wrapped in a filter fabric....then we set the tank. We also installed a dry well so we could monitor the dig and dewater if necessary...I will always remember the delivery truck driver, there were stickers all over showing NOT to remove the straps until the load was under control of the offloading contrivance, even had a sketch showing the tank rolling off onto the Driver....of course he shined all these warnings...