Yes, Eurocampers.com does show a grey water tank that can be used.
However, there are three major problems that you must solve: 1) making
and installing your own brackets to hold it on, 2) dealing with the
airconditioning hoses and 3) modifying the hole where the grey water
enters the tank. Thanks to a very creative and skilled fellow list
member, I have one on my van. I couldn't have done it myself. If you
choose to go this route, you had better be very skilled and have lots of
tools and materials.
Lee Kouns
87 Westy w/ grey water tank