Hi everyone. I'm hoping you guys can help me wrap my head around what's happening with my situation and why.

I recently purchased a condo and noticed the upstairs tub was completely stopped.I took apart the stopper and removed what appeared to be 10 years worth of hair and grime. The tub finally drained!

I left for a day and when I returned, my kitchen sink (directly below the bathroom) was full of debris (sand, pebbles, etc.). I took apart the drain and it was completely impacted with similar debris. I snaked it to 25' to no avail. Now when the upstairs tub drains, debris and water will come up the kitchen drain. All other toilets and drains on both floors work fine. The kitchen drain also previously worked fine.

Where is all this coming from? And why would only a few gallons flowing through the previously stopped upstairs tub unleash this torrent of junk? Unfortunately, I can't find the clean out and I'm fearing it's inside the wall of the garage below. Thanks.