Can’t pay you squat was a common expression when I grew up.
Meaning nothing. The big zero. 
Normally squat refers to a crouching position like you squat down to crap. Or you do squats in exercise.
How did it become a synonym for zero?
Where did zilch come from? Especially as a synonym for zero?
Origin:
1965–70, Americanism ; perhaps continuous with earlier zilch snafu, Mr. Zilch a character in Ballyhoo, a humor magazine first published in 1931; for sense compare zip3
zilch
“nothing,” 1966, from earlier sense of “meaningless speech” (1960), originally Mr. Zilch, (1931) comic character in the magazine “Ballyhoo.” Perhaps from U.S. college slang (early 1900s) Joe Zilsch “an insignificant person.” Probably a nonsense syllable, but Zilch is an actual Ger. surname of Slavic
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doodly-squat.
Origin:
probably euphemistic variant of doodly-shit, diddlyshit; see doodle1 , diddle2 , -y2
:smack: totally forgot it used to be doodly-squat. We always shortened it to just squat.
thanks Peter.
There was always a dismissive quality to squat. How much is my help worth? I can’t pay you squat.
Yeah that’s the way I remember it, diddlyshit > diddlysquat> squat
I guess squatter came from the same etymology?
Someone who lives somewhere illegally without paying.
No.
Etymonline also has a slightly different etymology on squat, meaning nothing:
Those could connect, as a previous post alleges that squat replaced shit in doodly-shit.
I personally always assumed that squatters were so called because they were literally squatting on the land, making it difficult to take. So thanks for the enlightenment, guys.