I moved into a house where there is an old bathroom, changed into a laundry room. The area where the toilet was is tiled over and all fixtures removed... I want to re-install a toilet there again. What do I need to do? How do tell if the sewer line is sealed off or something?

Of there was toilet before - and presently the toilet inlet hole is tiled over, it is relatively easy to do.

1. Locate the hole
2. Remove tile to expose the hole and closet ring. There may be newspaper with concrete over it pushed into the pipe, or perhaps an old towel. Carefully remove this make-shift "plug" so you allow as little debris entering the pipe as possible... )

Here, I strongly suggest you snake the toilet pipe just to make sure it is clear of debris or foreign objects that might have fall into the pipe. Then, I would bring in garden hose, insert it into the pipe and let it run for few minutes, making sure the pipe will absorb incoming water

3. Insert brass bolts into closet ring sockets
4. Set wax ring
5. Install toilet bowl onto the bolts and over the wax ring
6. Tighten up the bolts
7. Connect water supply to the tank ( assuming there is the old water supply behind the toilet )
8. Caulk around the base of the bowl

Now, your toilet should be fully operational...

Good luck... let us know how you did... Milo