The Medium reservoir is 66cm diameter(61cm at top, 52cm at bottom) and 35cm deep. The Large reservoir is 90cm diameter (inside measurement - 80cm at top and 73cm at bottom) and is 34cm deep. The access point in the lid is held in place by a small piece of fibreglasss which will need to be cut. The access cover plate can then be turned over and will cover the access hole. For orders over 2KG please see below.