How far should the pipe extend from the inlet and outlet tees? Posted on April 21, 2016 by Mark Peabody There is no set distance that applies to all tanks or regions. Prior to installing any septic tank, you should check with your local sanitarian for specific lengths for the inlet and outlet tees. Mark Peabody Are your cistern tanks legal in my state/province? Is there a direct correlation between the number of bedrooms and the size of the septic tank?