YOU SAID:

The cats came to the party to pee in the litterbox

INTO JAPANESE

猫はトイレに小便をするためにパーティーに来ました

BACK INTO ENGLISH

The cat came to a party to piss in the toilet

INTO JAPANESE

猫はトイレで小便をするパーティーに来ました

BACK INTO ENGLISH

The cat came to a party to piss in the toilet