Replacing sewer line

I am preparing to replace my old cast iron sewer line. I am going to use pvc, 4". I have a pvc cross to use to attach the vent, and to the flange. My question is to connect to the drain line itself, am I to use a 90 degree elbow? Will I be able to get the drain line to the proper slope by using a 90 degree elbow, or is there a special elbow for this? Any help would be great, thanks in advance.

Pictures would help in your describing of your situation.


I believe code in most areas that 90's cannot be used underground unless it is used to pass vertically through the concrete floor.