Yes, you can go outside the house and around to meet up with the sewer. You should go down through the floor (maybe cut a 1'x1' hole in the floor) then go through the foundation wall with the top of the pipe 18" underground. There should be a test-tee just outside the wall. Then maintain a 1/8" per foot fall to the existing sewer. Before you begin, you should make sure the existing sewer is below ground far enough to accomidate the fall. I don't know about your local codes so it would be a good idea to check with the local authorities first.