I have bathwater coming up through my "back" drain in my basement. I have NOT noticed any toilet water or sink water coming up yet.
I checked the drain in my back yard to the drain in question... no problem.
I checked the drain in the middle of my basement to outside sewage line... no problem.
So I am assuming the issue is from the "back basement" drain to the middle drain. Should I be snaking it or using a chemical?
Any advice would be great.

What's a "back" drain in my basement. Do you mean floor drain? What's it back of? Whatever it is you have a blockage downstream from it. Snake the line from that spot on. Good luck, b Tom

My basement has two drains... middle of the floor going to outside public sewers & in the back of my basement next to my steps that lead up to my backyard.
I flushed water down the floor drain that leads to the sewer lines... no backups at all.
I then placed the hose down the drain on question (yes----a floor drain), and it all came back up.
My guess is that it is between the back floor drain & the other drain.
But I do not see any toilet or sink water coming up (I colored used dye), just upstairs tub water... weird.

You're going to hafta dumb this down for me, Let's call the middle drain #1 and the back drain #2. Number one drain goes to the city sewer. But the only information you gave me about #2 is
& in the back of my basement next to my steps that lead up to my backyard This is the floor drain with a problem and you give me information about the one that works, What does #2 connect to and where does it drain to? Back to you, Tom

The upstairs water (tub) comes down through the pipes into the basement. Then makes it way downward out of the house & into the public sewage lines.

The basement has 2 floor drains in it. The water coming from the 2nd floor tub is piling up in somewhere between #1 & #2, or so it seems. That's where I am confused.
No water except rainfall is actually going down that drain, but for some odd reason it is coming up from it.
I have checked #1 & the water seems to go out to the sewers. When checking #2 (which drains downward into #1), it backs up.

When I reference rainfall going down "that drain", I am referring to #2-----which is the drain in question.

If your blockage's downstream from #2 then that's the place I'd snake from. Let me know how you make out. Good luck, Tom

I bought a 50 ft snake & snaked #2. All the sudden a big woosh & it all went down. I pulled the snake out & it brought a TON of baby-wipes. Must have been my 3 year old, although she's usually good with toilet tissue.
Thanks a lot for the advise, I clearly am NOT a plumber.
C-

NOTHING should go into a toilet that doesn't come from a human. Thanks for the update. Tom