Debbie,
What were his symptoms?
In many men, tamsulosin generates a 20% improved flow rate, which helps to achieve complete voiding. There are other ways which can work to achieve this, such as double voiding (wait for 30 seconds, and have another pee, and repeat until no more urine).
In other men, it's necessary to avoid acute urinary retention and emergency catheterisation.
Tamsulosin is usually provided in a modified release form to prevent absorption immediately, because you would get an instant overdose where you could collapse due to low blood pressure, followed by no effect because it's all gone. Even then, it needs to be taken with food, because otherwise absorption is too fast.
Guessing here, but I would have thought doing as the pharmacist suggested should work, but perhaps sprinkling capsule into water (but not dissolving) so there's more liquid to flush it through. Must be after food, and not on an empty stomach. Don't do it by grinding up or dissolving the pill or the capsule contents, as that would probably destroy the modified release property and generate an overdose.