Is there a direct correlation between the number of bedrooms and the size of the septic tank? Posted on April 21, 2016 by Mark Peabody In most state and county regulations or codes there is a direct correlation between the number of bedrooms and the size of the septic tank required. Please check with your local sanitarian or health department prior to purchasing any septic tank. Mark Peabody How far should the pipe extend from the inlet and outlet tees? Where can I find the installation instructions for my below ground tank?