Concrete floor and water ?

I posted the following yesterday in the DIY section, not sure that was the best place for it, so trying here, problem with sludge coming up from concrete floor, so any advice would be most welcome. Apologies in advance for the long post, just trying to explain as best I can:

Hope this is the correct section to post this in, I nearly went for the flood damage.

The property has concrete floors, however I have just spotted some thick black sludge, coming up from the garage floor. My first thought was waste from the downstairs toilet as it is roughly the otherside of the garage wall (internal garage attached to the property). Its a bit like oil and though perhaps some had been spilled but I'm sure its coming up from the floor as it wasn't on anything else.

Now it doesn't smell like or look (what I think it would look like) waste from the toilet, its more of a black sludge, oil like, which to me, points to a issue with water getting through the floor. I have checked the rest of the house but have not noticed anything untoward as yet (it was a quick visual check, lifting caprets / floor coverings where I could).

First question - Does it sound feasible that it is coming up through the floor? Its coming up where the wall meats the floor between the garage and the house (so not external) like in the middle. I also notice the floor in the garage isn't as smooth round the edges like they didn't take the top nice smooth concrete all the way to the edges.

Second question is what to do about it? Is it something I can claim on my insurance (buildings?) I've looked at my policy and I'm none the wiser to be honest.

Third question is what to do about it, should I try and get advice from someone in the building trade? Or should I just call insurance. I'm expecting to be told that the builders have not used the correct materials / concrete mix / waterproofing and best case is the entire garage floor needs to come up and be redone. The concrete in the garage is at a slighty lower level than the inside of the house. Although that means little to me, it could be the same thickness, have the same amount of waterproof compond (if that is the correct term) in it.


Grateful for any advice, the land round the house does seem pretty poor when I've dug the garden its does seem to have some clay in it and I am constantly trying to address moss on the grass.