What the poop?

So, to make this a short story, we recently moved in to a house in a small town where some feral cats have been hanging out. Turns out a mother cat (affectionately named by us "mama cat") has had 2 batches of litters; one with two cats that are now around 8 months, no longer feeding; and the second batch just teeny little kittens about 5 weeks old. We have been taking care of the feral cats (first batch who will not come near us) with water and really cheap cat food. Basically keeping them alive. The mama cat we feed more nutritional wet food for nursing purposes and the kittens who are now 7-8 weeks of age are eating dry kibble. The mama cat and kittens up to this point had been living on our porch for a couple weeks.

We gave mama cat and two of the kittens away last weekend. We have not changed the litter boxes since then. Mama cat had some diahrrea issues from who knows what and couldn't use the litter box correctly. It was a mess. We kept one of the kittens who is in great health and is now an addition to our family. We went on vacation with him this weekend leaving our other three full grown adult cats ( who are lovely and healthy and pretty) to hold down the fort. When we come back we begin changing litter boxes. 

What in the sam hell.... we open the main litter box and there is a pile of dried liquified dung with small chunks of solid feces, looked like cow dung, probably about the size of a cow pie too, literally the size of a server plate in the front corner of the litter. Biggest mess of cat dung I have ever imagined in my life.

Our three cats ate immediately and did so just fine as we fed them right away when we got home. 

We are not sure if this is from the mama from the last time she was here, but we are hoping that it is not our cats. I would post a pic but quite frankly that's not in good taste and we just bagged it up. Did not smell weird but just looked like somebody had the special of the week and had some explosive bowel movements in one big liquid pile. It wasn't sprayed. No immediate food changes or anything either. 

Could be the mama cat was sick from outside but what should we do to make sure it's not our cats? Are there signs they'd be sick like that?

Um, if you don't clean the boxes for several weeks there's going to be a lot of poop. Whether that was from one explosive event or several visits, who knows. But please, for your cats' sake, keep the boxes cleaner in the future (they should be scooped daily and changed/scrubbed whenever the litter is smelly after scooping). And it's also not generally a good idea to introduce strays of unknown health and parasite status to pet cats until they've been fully vetted.

yeah, I have three cats and honestly I have to change the litter boxes once every 3 or 4 days, because I'm just gonna come right out and say it, with three cats, not changing a litter box in over a week can get kinda gross, not to mention that most cats don't like using a dirty litterbox.
 

I have 2 cats and 2 huge litterboxes. I change them every day... There's no good reason not to. If a cat finds their litterbox too dirty they will use your floor. Once it starts, good luck stopping that behavior.

Ok, so there hasn't been one iota of useful information on this thread so far pertaining to my main topic. 

So, TO SOMEONE THAT CAN HELP - - 

What the hell is this liquified cow dung?

I am not sure that we can answer your question.  If we are reading your post correctly; no one was there to really observe what was going on with your kitties while you were away, so it's hard to say.  Is the litter box they use indoors or out?  Again; if I am reading this right, it's a box the mama cat potentially went in when she was here, but it was uncleaned till you came back from this weekend's trip?  There could be any number of issues to cause some diarrhea; which that is all I could think that would be.  Anything from a bug passed on from that Mama cat to one of your current kitties eating something that didn't agree.  

First of all there is no foul language allowed on this forum. It's not offensive to me, but it offends others so it's not allowed. That's why your swearing keeps getting marked out.

If I had to guess what it is, I'd say your cats were sick while you were gone and they all crapped in the same corner of the litterbox.

Seriously though, how would you feel if you relied on someone else to flush the toilet for you (b/c you couldn't do it yourself) and the guy only flushed it every couple of weeks?

I think what everyone is really trying to say is that it is too late, after several days, to identify precisely what happened, or, very importantly, which cat(s) were involved. Anything would be a guess. In a multicat household it is especially important to check the litterboxes at least daily and scoop them out, so you know immediately if there are any health problems. I can usually tell which of my eight cats has done what, so I know what to do if there is anything unusual. And you should never let a strange cat use the general litterboxes until you are sure there is no health problem and it has been dewormed.