Hey Coop-
We had a tub fabricated with a screen at the bottom and a spigut. After we distill on the grain, we pump the spent mash into the tub and place the spigut over our floor drain. After a few days, the grain is dry enough to shovel out. You just have to make sure in the warm months to get it out quickly because it can turn to a science experiment overnight!
As far as your water/grain ratio goes: I've had success with 160 gallons of water, 300 pounds of grain and 50 pounds of malt. 1 kg of dry yeast (493-EDV) ferments 8 to 9% abv at 85-90 deg. F in 72 hours. I'd like to try some different yeasts for whiskey to get some different flavor profiles, but the 493 is neutral and efficient for vodka. It's also easy to use, store and relatively inexpensive.
Hope this helps.