The sink faucet had broken and the spray hose had worked loose.

That said, I am able to get a hose about 20 feet or so into the drain with no interruption, but jamming it around in there isn't doing anything to get this thing drained.I bought a declogger that attaches to the end of the hose, but it doesn't seem to help in this.Anyone have any ideas?

While everyone worry about toilet tank to bowl gaskets, and shutoff valves, they are important.But don't forget about the washing machine hoses.

I found a hose running to a tenants unit upon further investigation.

LOL, James, you get me a wash tub, a narrow long board, some cord, some table spoons, a garden hose and a few oil funnels, some cans and trash cans and some sticks a few small rocks and a frying pan, we can jam!

His kids would turn on the hose in the summer time to play, get bored, then walk away with the hose still on.

You're getting hosed. 

I can make sure the right hoses are used, and that the connections are secure. 

Did I mention, it was very protective of it's territory and as a result had the ability to fire-hose his markings throughout the entire baseboards and sheet-rock of the entire house.Several weeks later, they moved out in one evening, which was the last night before their things would be left on the sidewalk.

I'd get a good roofer out there and have them take a hose up and figure out where the leak is.