Wild camping Orkney there are many places to empty toilets also water available.
The council run sites one Stromness and the other Kirkwall both have in the past have bee able to use for toilet emptying and topping up, As you are coming in spring 2011 I cant say if this available depends who the wardens are but will inform you early new year will also give a list of where to wild camp all the best.
Merv[
www.pentlandferries.co.uk
www.northlinkferries.co.uk