I'm in the process of remodeling a basement bathroom directly next to an exterior wall. Previously there was a shower and now I want to put in a bathtub. When I took out the fiberglass shower, I found that the shower drain was connected directly to the main waste line leading out of the house. The shower drain had no p-trap. It just 90 degree into the waste line. I also discovered that there was no vent pipe nearby for the shower. However on the outside of the house adjacent to the foundation wall is a vent pipe sticking out of the ground that is in line with the existing shower drain/main waste line. Also b/w the shower drain and outside vent pipe is a toilet. Is this the pipe that vents the toilet and shower? The distance between the shower drain and outside vent pipe is about 4 feet. Also right after the vent pipe is the whole house U trap.

My next questions is regarding the new bathtub drain. Does it need a P trap since the old shower didn't have one. If so, How far downstream from the bathtub drain can I put a new P trap and still be considered vented using that outside vent pipe. Reasoning being the new drain is going to be 2 feet further upstream from existing shower drain.

Sorry for the long post. Just trying to give as much info.

"My next questions is regarding the new bathtub drain. Does it need a P trap since the old shower didn't have one. If so, How far downstream from the bathtub drain can I put a new P trap and still be considered vented using that outside vent pipe. Reasoning being the new drain is going to be 2 feet further upstream from existing shower drain."
ALL FIXTURES having a drain are mandated by law to be trapped. Your bath tub has a direct open connection between the sewer and is exhausting sewer gas into your home as we speak. Sewer gas is dangerous to your families health and the methane content makes it explosive.

"How far downstream from the bathtub drain can I put a new P trap and still be considered vented using that outside vent pipe."
The trap must be installed directly under the tub waste and overflow. The vent through the roof to be installed after the trap.
You need to geta plumber out there to tell you exactly what you have to do to bring your home into code. Good luck, Tom

Hi Tom, Thanks for replying so fast. When I pulled out the old fiberglass shower and saw there was no trap, I did immediately cap the pipe.

So the vent pipe that is pretty much coming up right next to the exterior wall outside that is b/w the running trap and the existing shower drain is not venting the shower? If not what's it's purpose?

If I understand correctly the vent pipe must be before the trap.
I'm having a hard time picturing how a bathtub drain and p-trap should be properly installed. The tub drain comes down into the p trap then into the main waste line. Where should the vent pipe tie into this.

Attached is a diagram. Is this how it should be piped?

Can a running trap be used for the bathtub instead of a p trap?

Thanks again for your help.

"So the vent pipe that is pretty much coming up right next to the exterior wall outside that is b/w the running trap and and the existing shower drain is not venting the shower? If not what's it's purpose?"

If you can tell me what it's connected to I'll tell you its function.

"If I understand correctly the vent pipe must be before the trap.
I'm having a hard time picturing how a bathtub drain and p-trap should be properly installed. The tub drain comes down into the p trap then into the main waste line. Where should the vent pipe tie into this.
Attached is a diagram. Is this how it should be piped?"

No, the vent comes AFTER the trap,(see image).

"can a running trap be used for the bathtub instead of a p trap?"

No, The raiser from the "P" trap connects directly to the tub waste and overflow. A running trap is not configured to do this.

Good luck, Tom