As for the "huge" clump, I had the same thought as raecarrow...perhaps they used the same spot twice. I wouldn't worry too much about clump size, unless you find the clumps being too small or much smaller than normal on a regular basis, indicative of one or both cats not producing enough urine.
Also, it's not unusual for some cats to like to pee or poop in a different box, although my girls don't seem to care.
Yeah thankfully mine are always well-hydrated. They get two wet meals a day and actually drink water regularly since I've got one of those pet fountains which seems to encourage them.
Fusing makes sense! It just seemed so solidly formed that I assumed it was from one use. But considering how much time Apollo spends "tidying" I wouldn't be surprised if he helped some fresh clumps merge by pushing them all into the same spot.
The only unfortunate thing about the specified boxes thing is...the poop box always smells awful while the pee one smells like nothing. It wasn't so bad with just Apollo, but Athena's tummy is so delicate that she occasionally has...unpleasant bowl movements if she eats anything
she's not supposed to. Which she manages to do often.
I'm surprised if my cats do anything IN the box! I had to eventually get a plastic mat to go all the way around the box... Nebbie has this thing of poop right outside. She'll stand facing the box and go right outside of it... it's not as if her aim is bad, because she doesn't have a single paw even IN the box!
Paizly pees wherever, but I think that's because it's territory issue....she doesn't like Nebbie much. I do have multiple boxes, but unless I can get Nebbie to quit using one and leave it JUST for Paizly, I guess I'll just have to keep lots of Natures Miracle around.
Haha aww, I can imagine that's frustrating. Thankfully both of mine are perfect about using their boxes, but because of Athena's digestive troubles, she occasionally has soft poo which she then steps in and tracks about, or she'll have managed to swallow something like a carpet thread and end up with a "stringer" that she proceeds to drag across the floor and deposit on the carpet.
Apollo has an iron stomach and good litterbox habits, but Athena's system is a delicate balance. If one thing is off, the results will be messy.
I often find Apollo cleaning her off because she's not great about cleaning herself either.