Comes from the childrens nursery rhyme:
Number 1, tickle my bum
Number 2, do a big poo
Number 3, go for a wee
Rhyming slang for doing a pee or wee (urinate)
In the same way number 2 is rhyming slang for poo.
Had too much to drink, gotta go number 3.
The act of making thick in the warm / doing sex on a lady / putting your choo choo train in a womans tunnel
Im gonna make sex on a lady and number 3 in her warm
Menstruation and/or menstrual blood.
Suzy was relieved when she finally had her number 3.
Number 3 means full sex with a woman. Ask and agree = three - rhyming slang.
Men often visit prostitutes for Number 3
The act of performing an abortion on a toilet, flushing down the fetus.
Sally was in the washroom for a long time because she went number 3.
To vomit into a toilet. Typically done after a long night of drinking.
"Gross...someone's number 2 is gonna make me go number 3!"