I have already poured a 6 inch thick concrete slab for a shop floor. During the slab construction a 3 inch pvc rough stubbed drain was put in the concrete to act as the shower drain (from the shower to the septic tank line). I realized after the fact that no p-trap was placed within the slab; only a fitting to mate the shower drain to the pvc and a 90 sweep L to a short piece of 3 in pvc that is stubbed to the outside of the building. Nothing has been connected to the septic tank drain lines.
QUESTION-is there a way to add a p-trap to the outside of the building before the shower waste enters the main septic drain lines? If so, is this 'just as good' as a traditional p-trap directly under the shower, and will it work as well? I really don't want to cut the slab to do this.
Thanks.

Hey John,
"QUESTION-is there a way to add a p-trap to the outside of the building before the shower waste enters the main septic drain lines? If so, is this 'just as good' as a traditional p-trap directly under the shower, adn will it work as well? I really dont want to cut the slab to do this."

You're going to love my answer. You're looking to install a (see image, this image is a small PVC running trap. You'll need one in your pipe size and material, but you get the idea.) running trap, (not a "P" trap) in your drain line. This will give you a trap seal for your shower although the shower drain line will be open to the air from the drain to the trap. This should not present too much of a problem but I thought I should mention it. Good luck, Tom

Wow, thanks for the super fast response.
One additional question. I like the idea of the running trap (I have actually done this before on another project). I assume this type trap is OK to have outside of the building. I am not sure I understand what "although the shower drain line will be open to the air from the drain to the trap" means.

' I assume this type trap is OK to have outside of the building"
That's about the only place they're used.

"I am not sure I understand what "although the shower drain line will be open to the air from the drain to the trap" "

All that means is instead of just a few inches from the drain to the trap seal in the "P" trap you will have X ammount of feet from the drain to the trap seal of the running trap. This will give you more pipe to pick up odor. This is a "trade off" from having to jackhammer up your floor. Your choice, Tom

I understand, thanks for your information and time. Much appreciated.
John