I have just bought a split-level house and on the lower level (on the slab) there is a laundry room and a two-piece toilet, side by side. So I have a lavatory and toilet, then a partition wall, and on the other side a laundry sink, washer and dryer. I would like to get rid of the laundry sink, put in a stackable washer and dryer and add a shower in the space obtained. How do I find out where the existing pipes run, and what's involved in putting in the shower? I have done some plumbing before, but not involving concrete and below grade work. I would really appreciate any advice.

Hey Raven,
Leave the washer set up alone, you'll be using it to run your over and under, and cap off the laundry tray drain. Leave the water alone as you'll be using it for the shower supplies.
You don't have much choice but to jackhammer up the slab and locate the lavatory drain and connect to that so your shower will be wet vented. I wish I could give you the easy way to connect the shower drain which would be to use the laundry tray drain but I'm afraid the washer and laundry tray's using the same line. With the laundry tray drain at set 18 or 20" above the floor line there was no problem with the washer discharge, but if you tie in a drain at floor level I'm afraid the washer will discharge into the shower. So I 'm more comfortable connecting to a fixture that doesn't discharge with so much force and volume.
As for figuring out where the pipes are under the slab, we usually locate the house main by where it exits and then figure how we would tie the branch drains to it if it were us doing the original job. Sometimes we're even right! LOL! Good luck and if I can be of help just click on back. Tom

Thanks much, Speedball. I don't have much choice but to move the washer to locate the shower so I'm going to be doing a fair amount of concrete breaking in the area which should reveal where the lavatory drain is coming from to the main drain. But you know about the best laid plans.. . I'll probably be back! Thanks again.