my upstairs bathtub has been slow draining and sink drain backs into the tub

 its steel pipe. I replaced the tub and sink a year ago and cleaned the pipes all out before I installed the new ones. The drained a lil better at first but have gotten progressively worst. Its galvanized pipe that has been there for 60 years. The tub doesn't have a proper pee trap beacause there is not enough room for one so I put the same one that was there back in.

 I don't believe it would be so bad in just one year, it looks like the stoppage is below the level of the pipes you dealt with last year.

How is the toilet draining, does it have its own T at the riser or does it flow into the same pipe horizontally (I mean gently sloping downward, not literally horizontally), then goes into the riser stack together with the drains of the tub and the sink?

You may try to run the auger through the toilet and see if it makes any difference. If not - then have to go up on the roof and auger through the roof vent going straight down. If the first floor bathrooms (if any) do not have this issue, it would be in the main stack before it hits the first floor Ts (see the diagram attached).

There may be a cleanout on the second floor or the attic that may save you a trip to the roof - if it's above the sink level, I would open it and feed the auger through there, much more convenient than the roof, obviously. I would <strong>not</strong> open any cleanouts below the second floor bathtub drain.

 Thank you.

my upstairs bathtub has been slow draining and when I run water in the sink water comes up into the tub. It smells bad and is black.

Try to consult the professionals regarding the matter. Or maybe pour some vinegar on it, it will help unclog the drain.

This often happens  in every house hold. I am glad that you have addressed this issue. I have learned a lot form the comments below. I'll keep visiting for more of your  posts.