411. Permanent vs. Temporary Restrooms
Tefillin, Mezuzah v’Sefer Torah 4:18
The previous rule (about what to do with tefillin when entering the restroom) refers to a designated lavatory, where he will not get sprinkled by drops of urine. In the case of a space temporarily being used as a lavatory, one may not enter with wrapped-up tefillin in his hand. In such a case, one should remove his tefillin and give them to a friend to hold. (Editor’s note: obviously, this was long before indoor plumbing. Nowadays, pretty much all our bathrooms are permanently-designated as such. Perhaps a “port-a-john” would be considered a temporary restroom.)
Tefillin, Mezuzah v’Sefer Torah 4:19
If a person is wearing tefillin in the late afternoon and he must use the restroom, so that there will not be time left in the day to put his tefillin back on after he finishes, he may not enter the restroom with his tefillin wrapped up in his clothes. In such a case, he should remove them and place them in their case if it is a handbreadth in size, or in another case that is not designated for them even if it is not a handbreadth in size. He should hold the case in his hand when entering the restroom. Similarly, if one needs to use the restroom at night, he should place his tefillin in a container and enter the restroom holding the tefillin in his hand.