פירוש על ברכות 46:3

Viz. that a man may not urinate while holding the Tefillin.

So above (fol. 23 a, p. 150) where Bet Shammai teach that the Tefillin must be left on the window-sill

See above, fol. 23a, p. 150.

Since it is solely for the purpose of urinating, it is assumed that the Baraita refers to an occasional privy.