As written, it "feels" like an American expression.
The polite expression in English is "I have to wash my hands".
(Ladies used to "powder their noses" but I don't think that expression is still in common use.)
[In parts of Africa, the equivalent is "I have to wash my feet", but in the vernacular, not in English.]
However, your expression seems to be a deliberate reaction against polite expressions and I think would be considered rather vulgar/rude/offensive in most circumstances. Perhaps it would be amusing in some company.
Perhaps AE speakers would be better judges of these matters ...
Hope this helps.