I had a look at this link.
The problem is the orifice is located on the bottom of the tub, instead of the side. The water jet will project downwards, instead of with an X and Y component (as mentioned in the article).
Are there any other methods of calculating the coefficient of contraction of a orifice where the orifice is located on the bottom of the container or do I just have to estimate ~0.62 etc.
See here to see my experiment.