YOU SAID:

I farted and a poopie almost slipped out

INTO JAPANESE

オナニーしてウンコが出そうになった

BACK INTO ENGLISH

I was masturbating, and I was about to poop.

INTO JAPANESE

オナニーしてウンチしようとしてた

BACK INTO ENGLISH

I was trying to masturbate and poop.

INTO JAPANESE

オナニーしてウンチしようとしてた

BACK INTO ENGLISH

I was trying to masturbate and poop.