Sheikh Sâmî al-Mâjid
The supplication to enter toilets should be read before entering, not after. It is disliked to mention Allah’s name in toilets or bathrooms due to the respect that should be given to Allah’s name.
Ablution should be performed outside of bathrooms. It is permissible to do so inside in case it is otherwise difficult. Mentioning Allah’s name before performing wûdû’ in the bathroom should be pronounced in secret – since some scholars are of the opinion that mentioning Allah’s name is obligatory unless the worshipper unintentionally forgets to do so.
The supplication to be made after relieving oneself and the one to be offered upon the completing of wûdû’ should both be recited after leaving the bathroom.
Source: Islam Today