How do you plan to press them after washing them?
You may be surprised how difficult this will be.
The issue with washing tailored trousers is that pocketing, curtain and interlinings all respond to washing in different ways. Even the thread could shrink and create puckering on every seam.
If the thread or any of the other materials in the waistband construction or the curtain and pocketing shrinks, you may not be able to restore the trouser to the original...