Finishing up an honours project dissertation, discovered an engineering law that means the majority of the designed system isn't needed, what do I do?
Torricelli's law/theorem is not an engineering law (which could be interpreted as having some legal aspects); it is a fundamental result from the physics of fluid flow.
The closely related theorems of Torricelli and Bernoulli are useful starting points for engineering work, but nothing more, since they are highly idealized and involve many assumptions. These assumptions have to do with compressibility of the fluid, friction during flow, wetting of the pipe walls etc.
Since you're doing experimental work, you can actually investigate how much these factors actually affect the intended use  and therefore establish how adequate the theoretical law is. If you focus on it from this perspective, I think your results can be valuable.