I juiced my melon yesterday, and if anyone is curious, all I did was slice the melon in half, scrape the guts out with a large spoon, put the guts into a blender, mixed on low/med speed until there are no chunks left, and put that through a BIAB paint strainer style bag. Once I had the strained liquid I added 1 Campden tablet into 1 gallon of juice, and sat it in the fridge. It's been there over night and I have noticed some sediment settling out. Probably leave it in another day then put it in the bottom of the keg. I'll let you know how it turns out.
I tasted the pink sludge too. I thought about racking something onto it in a one gallon fermenter but decided against it (for now at least). I only stained the juice because it's going right into the keg and I figured all of the goop would fall out of suspension and get pushed out in the first yeasty pints anyway. If I were going into fermenter I probably would have just tossed the un-blended guts right in.
This batch had a few uncommon variables for me. I've never used this juice for cider before and I've never juiced a melon before. Hell, I've never used any fresh pressed fruit juice before other than apples for pure cider.
The base cider was fermented from store bought 100% unfiltered apple juice with about 2 lbs of dark brown sugar and fermented using my "house" strain of nottingham cider yeast (probably about 3 or 4 generations in). It was left in the fermenter for probably 2 months and the result was a very dry, tart, thin, and extremely cloudy cider that absolutely refuses to clear. Mind that I used no clearing agents and the juice was just as cloudy at it's point of purchase so I didn't think much about the haze.
At kegging I poured one gallon of watermelon juice (with one crushed campden tablet added (had been refrigerated for probably 2 days and still tasted and smelled great)) into a sanitized keg through a sanitized funnel (maybe I should have siphoned it in more gently) and then racked the cider onto the juice.
I did fill the keg awfully full so that plus cider's tendency to take longer to force carb than beer probably explains why it's so reluctant to carbonate (right?).
The remainder of cider I kept still in the fridge is great. Still cloudy as muck but tastes fine.