Expert: Sharon McCarthy - 11/3/2009

Question
Hi - Soon I will begin finishing a bathroom in our unfinished lower level.  We are on a slab and the house is 14 years old.  How would I know if the drain has a p-trap beneath the slab.  The pipes are roughed out for everything along with a vent, but no clue about the p-trap.

Answer
Dear Jacob,

  The only drain that would need a trap under the slab would be a shower drain. Is that what you are referring to? A toilet has it's own trap built into the bowl, and a sink would have the trap just under the pop-up assembly inside the cabinet.

  If there is a pipe roughed in for a shower drain in the floor I'd think all you'd have to do is pour a quart of water down the pipe, then look down with a flashlight. If there is a trap at the bottom, you should be able to see water down there. If there is a trap, it should be glued onto the end of the vertical pipe going down.

  Tub and shower drains should be 2" diameter pipes, just like drains pipes for washing machines. Most homes in my area are built on slabs. I've had to clean out hairballs and pull out combs from shower drains. As I recall the pipes go down maybe 12" or so, then bottom out in a trap. In all cases, I could look down and see water sitting in the trap. See if this works for you. Sharon