Grub, The noise can be delt with. You just need to add durso/stockman standpipes to the rear box. that shouldn't be a big deal.
Lets just get the thing draining first. Fill the DT up to the OF and the sump should be a good couple inches above the pump. You can also lower the inner OF box a bit so you can see if the DT going to overflow. The inner box just gives you the water level in the tank, nothing else.