Have a upstairs bathroom . The floor is pored concrete. This home is the second home in Piqua ohio to have electric. The bathroom is over the intrance way of the home. I have knocked out the celieling which is very old plaster, and found the line from the shower and sink goes to a trap , I think and them goes to the toilet. It is leaking in the trap or where the sink and shower meets befor the toilet. Its is the old black pipe, not sour how to put new back and what to use. And the old trap,or the connesction where the sink and shower come to gether has a split where they conect to both right in a floor joice. how to fix
You're saying the sink and tub flow into a P-trap, you think.
If that "thing" looks like this:
then it's called a "drum trap", and is what was used before P traps became the norm.
In this case you've got some ancient plumbing, and the way I would look at it is this: You can save 90 percent of the cost of maintaining your home by doing all the simple and easy stuff yourself.
But, in this case, I think we're talking about something that falls into the other 10 percent category. Most likely, that plumbing pipe is probably made of lead, and it might be best to replace all that old drain piping with new materials.
Yes, this may be a job for a plumber.
You need to completely rebuild your drain that services the shower/bathtub and the sink.
Later, you can finish the floor or ceiling yourself.