After things thawed out in Texas, I found that my kitchen sink will not drain. In checking the p-trap, I found the inside plumbing corroded and replaced all of it from sink drains (double sink) to stub-out. I have run a snake through the stub-out and down to what seems to be the right angle under the slab. I can not get past that, but there is nothing getting caught on the snake. I just can't get it to turn another corner. I dug up outside, removing a concrete step for access. I have actually run a garden hose in about 10 feet downstream, and have another access hole 20 feet beyond, where I can see water running freely. I have tried putting boiling hot water in the sink and plunging. I sucked out a bit of grit and slime, but not much. I need an idea on how I can go upstream from the Y shaped access hole. Water left in the sink will drain overnight, with no sign that there is a leak. I.e., it must be seeping slowly through the pipe.