I've found Water Fasting with senna tea useful for after I've been on a toxic food binge(I'm gluten and lactose intolerant and I kick myself every time I cheat) and I was carrying around about 5lbs of water weight from my body's near allergic reaction. However, I'd suggest you prep for a week with good healthy foods at the very least. Think of it as a veggie/fruit fast, then onto a short water fast, then back to the veggies/fruit. I water fasted for two days and managed to flush the last of my belly bloat(not real weight.. I was carrying around what looked like a pregnant belly full of air).
And definately think of previous attempts as baby steps to doing better on the next one. You can never know completely how your body will react until you try, and letting it derail you is fine, as long as next time, you plan to avoid that problem.