Gray tank plugged, limited options

Hello fellow RV'ers. First time utilizing Sony type of forum. I recently had the same issue. My galley grey tank was clogged with calcium, grease, food ect... after cutting the pipe under the tank and placing a double fitting problem solved. I am however, having a issue that continues to occur after that four order of a clog has been resolved. I had the carpet and padding pulled out and vinyl planking put in. I have a sludge like substance seeping up through the cracks in the planks. It hardens like tar and is so foul smelling. I clean it and it returns. This is actually how I discovered that I had a clog in the galley grey tank in the first place. After the clog was removed and the smell under my rid subsided, I am left with this sludge. I am very hesitant in removing the flooring to expose the wood underneath. Does anyone have any suggestions as to what to do. Or even what ot is. My fear is that the clog was there for years and it seeped through the wood floor causing mold and just plain garbage water to soak the wood. I should say I'm a first time rv owner and live in my fifthwheel year round. Also I'm a 48 year old woman who has fixed everything that has occurred myself. This one though seems a bit daunting. Help?????