You can get portable blue totes to use as grey tanks. They're available at any RV Store and at Camping World and come in various sizes. I suggest the units with four wheels and side discharge so you won't need to lift a full tank to dump. My unit does not have a grey tank either and I thought this would be a real hassle, but it's not that bad.
"If the women donít find you handsome, they better find you handy.Ē Red Green.