If it's an abscess, flagyl won't heal it or make it go away. But it will help with the rectal inflammation. My crohns responds good to flagyl, so hopefully it will calm down your inflammation. As far as the taste goes, there is nothing worse! This is how I take it, I take a drink of choc. milk, pop the pill in and then chase it down with more choc. milk. I don't taste it that way. I think when you take it with wter, it starts dissolving in your mouth. Someone on here wraps it in a fruit roll up and then swallows it.
You really need a good colo-rectal surgeon to look at your bump. If it is just an abscss right now, then it needs to be surgically drained in an operating room, cleaned out, and then left open to heal from the inside out. My surgeon also inserts dye in the abscess and then looks on the inside to see if there is any connection (fistula). If you just leave it, it will more than likely fistulize and then you are going to have bigger problems.