I finished my basement, installing a full bath. I was convinced there was no p-trap under the concrete, so at first, instead of breaking up the concrete, I was going to create a box with the s-trap underneath. When I did this, the water went down, but then after about a 1/2 gallon of water, it stoped draining. I then thought there was a p-trap or s-trap under the concrete. I still had to break some of the concrete an move the drain a little, but I didn't dig very deep. I put a nail on a string and droped it into the drain and heard water. This made me think there was a trap down there. I installed the shower, but now we ocassionally smell sewage. The smell is faint, gets a little worse when you turn the water on, but then goes away. We don't use the shower really at all, so is it possible the water is just evaperating, or is their now trap. Is there a device or something, I could insert in the drain to act like a trap? Any insight into this long, garbled mess would be great!!!