I would think that piercing the urethra would be painful enough the the "process" for the night would be ruined. However, there is the consideration that the injection site may not have closed.
I was told to hold pressure on the injection point for no less than five minutes, reason being to prevent bruising. Could leakage be a possibility if that step were skipped? Possibly. Could there be drops of medication still in the needles as it is removed that drips on the skin? Sounds possible.
I've not had a warning about oral sex and Trimix, but I guess it would not surprise me. I would talk to your compounding pharmacy as the ingredients vary for all of us.