So according to this study it appears that this risk exists if you receive rimming (having your ass licked).
The study was done in men who have had sex with men but are never penetrated in anal sex.
And surprisingly up to 10% had rectal chlamydia and 14% rectal gonorrhea. The only sexual practice they were able to identify as a risk for this was having received rimming in sex.
If you’ve been in this situation, don’t’ forget that when you next do an STI checkup to ask that they take rectal samples too, because a urine sample is never going to detect a rectal infection (or a throat infection come to that). Please do write to me if you need these points clarifying.