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 one's 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.
"Dude, I don't want your backwash." (This person has perhaps declined someone's offer of their nearly empty can of Coke).
by Hari____ April 12, 2006
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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.
Soph: Can I have my coke back, now?
Tat: Yeah, here you go.
Soph: Is that backwash at the bottom?
Tat: Er...
Soph: You keep it.

(incidentally, if anyone gets a bottle with backwash in the bottom, try refilling it with its original liquid as well, so it's full, then heating the bottle from below. Because it's seperate, I wonder if it behaves like a lava lamp. If anyone wants to try this, feel free to enlighten me.)
by ANBY June 17, 2004
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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
Someone eats a carrot sandwhich and becomes an arsehole by taking a mouthful from their cup and spitting it back in which bits of bread and carrot go into the drink with saliva=backwash
by bread infection October 22, 2005
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drinking something and spitting it back out into the bottle
eww you backwashed that, i'm not gonna drink that!
by j00l.i.e April 26, 2003
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When a girl washes your back in the shower.
Girl: Hey can I hop in the shower with you ;)
Guy: Yeah it's been a while since I had a good backwash.
by superkang December 9, 2010
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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.
So, Mr. President, pay no attention to the people that say the glass is half full. 32% means the glass -- it's important to set up your jokes properly, sir. Sir pay no attention to the people who say the glass is half empty, because 32% means it's 2/3 empty. There's still some liquid in that glass is my point, but I wouldn't drink it.

The last third is usually backwash.
by openedsource April 30, 2006
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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 friend's backwash and dating your friend's ex.
Also known as the second-hand spouse.
"So on Friday I'm going on a date with Evan."
"Girl, I wouldn't even TOUCH that guy. He's a major case of backwash."
by S J Thomas May 22, 2008
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