back out a big greaser

A colloquial expression, usually used in (but not limited to) Australia and similar/English speaking nations, for the process of defecation. Generally associated with humans and other humanoids, this phrase can be also be used to describe the defecation procedure of other animals eg. the family pet. A similar, slightly less descriptive version is the phrase back one out. Note that the word greaser has a wide range of usage in other contexts.

I really need to "back out a big greaser"
Watch where you step mate, I just watched Fido "back out a big greaser"
When I wake up I usually need to "back one out".