Backwash

[Vania]

[Backwash] is often created inadvertently or unintentionally when liquid escapes the mouth during the process of drinking, though it can also be created intentionally by an act of spitting or purposely letting liquid fall from ones mouth and back into the [container].

When multiple people drink from the same container, there will usually be some amount of [backwash] put back into the container; as the number of [sips] increases, in general, the concentration of backwash also increases.

[Renato]

to take a [mouthful] of drink from a container (cup/glass/bottle) and [spit it out] back into the container in which saliva and bits of food go back in with [the drink]

[Justin Bieber]

The [filmy], [cloudy] residue at the bottom of a drink that you get when you pass a drink to someone else. Always seems to be at the bottom, separate from the rest of the drink, like [oil and water].
Also a good way to determine if someone has eaten fish or tomatoes recently.

[Oralee]

When a guy or girl cums in your mouth and you [hold it in] your mouth only to [deposit] [the goods] into their mouth

[Little_Girl]

drinking something and [spitting] it [back out] into [the bottle]

[Donald Trump]

The [sediment] and/or [particles] of whatever youre eating that [ends] up in your drink.

[Merna]

[A George] W. [Bush supporter] characterized by drooling, religious [fanaticism], racism, homophobia, hate of others and self, ignorance, and an inability to think for themselves, with the intent to destroy anything or anyone different than themselves.

[Dianne]

A term that defines a person who has dated an [unimaginable] amount of people, usually all in the same social group. The term is used because of the [similarity] between the feelings towards drinking your [friends] backwash and dating your friends ex.
Also known as the second-hand spouse.

[Rihanna]

Backwash in Surfing. Describes a wave that reflects back to sea.

[Tariq Zaki]

the backward movement of waves, or the backward movement of water caused by something, such as a boat, passing through it: