As specified here, we have a solution of #"70% (v/v)"# ethyl alcohol. If we have a volume of #150*mL#, then, clearly, there are #105*mL# ethyl alcohol present. We assume, reasonably, that the volumes are additive.
So what of the other #45*mL# that is NOT ethyl alcohol. Well there would be some water, and there would also be so-called denaturants. These would include methyl alcohol, benzene, toluene, castor oil. None of these additives would interfere with the spirit's primary function, i.e. cleaning and as a disinfectant. If you drank it, however, it would make you blind. The fact that it is not drunk (except by those poor, derelict individuals who are so far gone in their alcohol abuse that would drink anything) means that you can sell the alcohol without charging tax or duty on it.
Are you happy with this?