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.
Sorry to hear about the abcess. I had a perianal abcess before I was diagnosed with Crohns 9yrs ago. I know how painful it is. I work for a doctor and he drained my abcess several times before sending me to see a proctologist who informed me that it was actually a fistula. Once I had the fistula removed It took about a month to heal, of course it probably took longer to heal due to the terrible flare I was having, but didn't know it was Crohns at the time. I know once the abcess starts draining it really relieves the pain. You said the hot soaks really didn't help but you might want to keep trying it several times a day to try to get it to drain on its own. Good luck I hope you feel better soon.