BUILDING AN EXTRA BATHROOM IN BASEMENT
Do I need a special permit?
Do I hire a contractor and how to find a good one?
PattyB is right. (I'll be saying the same think in 'other words' ...)
If your toilet (and whatever) is BELOW the current Vent Pipe in the yard, then if you were to get a sewer backup, your basement will be the FIRST place the 'stuff' ends up. Remember, sewage takes the path of LEAST resistance. This is why the Vent Pipe is the LOWEST point in the existing system. If you 'buck' that rule, you'll need to counter it w/either an upflush system or a one-way ball stop.
Yes, I'd hire a plumber to at least to the work to Code. From there, if you're game, you can do the finish work (and save some $$$.) Oh, and don't forget to update your Homeowner's Insurance for Sewage coverage ...
My best to ya and hope this helps.
Jay J -Moderator