I have a bathroom that has two sinks. The drain on both of them is
slow. I have tried all the various drano types with little or no
improvements. I tried using a water balloon thingy that attaches to a
hose and inserted it deep into the vent pipe from the roof until it
reached the floor. I was thinking that the water pressure will blow
out the obstruction and to my surprise the water overflowed from
another vent pipe inside the attic that I did not know existed because
it is burried under the AC/furnace train. Needless to say that
backfired. Now I am at loss of how to proceed. I know I have an
obstruction (probably hair) that is far down the drain. I would like
to use a snake but I am afraid that I could not tell where the snake
will end up because of the maze of drain pipes and vent pipes behind
the wall. Any ideas?

Thanks,
Joseph