If you are using Revit MEP 2009 select the fitting, right click to draw pipe, on the options bar set the slope and drag away the direction needed and click. You can also create a section offset slightly from the fitting and draw in section if needed using slope setting in the option bars.
This is a good way to stub out the pipe from the fitting and then extend the pipe from that point. Then use a little auto routing if you dare.
David