I had anal sex and 15 ish minutes later i had to run to the toilet because yellow watery liquid was coming out of me. there was a lot of it. ive never had this happen before and it was maybe two minutes of intercourse?

I would assume that the intercourse with attendant irritation of rectal mucus membrane caused a discharge of mucus mixed with some watery stool. If there's no pain,blood or continued discharge of large amount of rectal mucus, I think you can sit tight at this time. See your physician for examination as needed.

From the rectum or vagina? What does "a lot" mean? If something like a cupful or more, I would worry about internal damage to the rectum with possible penetration into the bladder, especially if you are new to anal sex. OTOH, such a problem usually would be very painful; absence of pain would be reassuring. Get care ASAP if it continues, if pain develops, or if any doubt.