I'm redoing a bathroom with separate tub and shower stall that are adjacent to each other atop a slab. I need to adjust the location of the tub drain for the new, wider tub. But what I found when excavating to expose the drain line was just an elbow that turns in the direction of the shower drain. The shower drain appears to have a trap from looking down into the drain, but there's no opening in the concrete surrounding the shower drain to know for sure how or whether the tub drain line is tied to it.

So my questions are whether the original plumbing was done incorrectly (shouldn't there always be a trap at each fixture)? If I do install a p-trap where there was none, and if this new trap and the one for the shower wind up being in series on the way to the vent stack, am I creating a problem? If installing the new trap is a sound idea, it would solve my drain position relocation problem as I could just angle it over toward the centerline of the new tub.

The original plumbing did work all right before... shower drain would get slow when it was fouled with soap scum; tub never had trouble draining. No odor problems from sewer lines (plenty of odors from rot from crappy job someone did installing incompetent shower pan that failed... the whole reason I'm in this mess.)

Thanks for any advice... hope my description makes sense.

Tub traps can be a running trap just out of sight past that elbow. Do you get sewer gas from this expose drain? From what you have said, no smell, you are probably OK from the trap aspect.

I'll see if I can't excavate a little further and feel or see what's there. Thanks.

I think Bob meant to say drum trap ,(see image)instead of a running trap.
Drum traps were installed in older homes and were left unvented. Back then the tubs would vent out of the tub waste when draining, Glub! Glub! Glub!
Follow the drain line and I'll bet you'll run into a drum trap. Good luck, Tom

Tom, are drums buried in a slab? Don't have much experience with this, most home I have worked on were all built after 1970.
Thanks,
Bob

No odor problems from sewer lines That's what the OP claimed.
And that's why I believe it's trapped. If it weren't he'd be complaining about a smelly drain. Although I've seen plenty of drum traps installed in older homes I havenever seen one installed with a running trap. At first I thought the plumber might have " jacklegged" the tub drain into the shower trap raiser but the OP looked down the trap and didn't mention a tee so I figure there's just got to be some sort of trap on down the line. What's your take on it? Tom

Just have not run into a drum trap under a slab before, figured it must be a running trap but not sure.