Installing P trap through basement floor
I bought a house with an unfinished basement and three drains capped off in one room. I was told this wasd to add a bathroom. Next to the shower drain was a cinder block buried in the concrete filled with gravel. I was told this was to install the P trap for the shower drain. I busted out the cinder block in the concrete and dug around and looked with a flashlight under the foundation. The drain pipe from the shower is going into a WYE drain and the other end is capped which was under the block. Do I cut the drain under the concrete and install the P-trap immediately under the drain and tie into the line? Why isn't the p-trap just installed while the builbers are building the house?