The only way of doing it that I can think of is to bury a plastic barrell in the ground near to your bathroom and place a submersible pump into it.You then pump the grey water from the barrell in the ground into an I.B.C 1000 litre jobby !! You can then just open the 2 " tap then when you want to get the water out. Also there is no reason why you cannot save your rainwater into a BIG water butt. Just get the heights right and you can run the pipe between the diverter and the tank as long as you like, mine is at least 35 yards. see www.simplesprinklers.bravehost.com to see what I did.