It's a straightforward and direct way to say it. If you want to be more polite or formal, you could use:
* "Nag-ihi siya" (He/She urinated) - This is a more neutral and polite way to say it.
* "Nag-punta siya sa banyo" (He/She went to the bathroom) - This is the most polite and indirect way to say it.
It's important to consider the context and your relationship with the person you're talking to when choosing the appropriate phrasing.