@ coryg – I doubt if the results will be very accurate if for no other reason than the ph of the water in your toilet will vary on a regional basis before you add any urine to it. Urine will also vary in depth of colour depending on time of day and individuals. The ratio of water/urine/cabbage water would need to be consistent and I have also found when measuring the ph of a sample of water in the fish tank that the quality of light also affects the results – natural daylight is best. So, all in all, I would class this as a school experiment and no substitute for using commercially prepared tests if you had cause for concern. Interesting though.