Chapter 82:12
Carrying from One Domain to Another
12. A person should not stand in a private domain and spit or urinate into
the public domain or into a "carmelis." Similarly, it is forbidden to do
so from the public domain or a "carmelis" into a private domain, from the
public domain into a "carmelis", or from a "carmelis" into the public
domain (1).
It is also forbidden to walk a distance of four "amos" (approximately 2.2m)
in the public domain or a "carmelis," or to walk from one domain to a
different domain, with spittle that has accumulated and has been moved
around in one's mouth, [and is ready to be spat out] (2).
FOOTNOTES:
(1) Spitting or urinating is considered the equivalent of picking up an
object in one domain and putting it down in another domain (See Shulchan
Aruch 350:2, and Mishna Berura).
(2) Since the spittle is ready to be spat out, walking with it in one's
mouth is considered carrying (Mishna Berura 350:14).