if you're planning to hook up to a septic system down the road, with a poured slab floor, you'll need to layout the plumbing before you do your slab.

you CAN cut concrete to add that kinda stuff later, but its a messy process at best, and i would have to imagine it to be expensive.

making sure you have your pitch and whatnot right is going to be important, so at the very least you'll want someone with underground experience to assist with the layout and placement.

at the very least you'll need to plan to accommodate a drain for a toilet, a shower/tub, a bathroom sink, a kitchen sink - and more than likely some kind of laundry area unless you plan to wash your duds at the local 24 hr suds-o-rama anyway smile

the good news is you can stub the pipe up above the floorline and just cap them off until you're ready to use them. you can do the same outside, just get it a stick outside of your outside wall and stuff a 90 on there and come back up so you know where to start digging to connect your septic system.

this is probably going to be something you're gonna want to get a professional involved with to make sure you dont have to go back and redo it due to it being buried under the concrete.
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