It shows the high speed as optional but its required for us. Typically all lines are -6 after the pump. The secondary bypass can be optional on 305's some run one and some don't. Some guys run more than one line back to the tank. Others run the main, secondary, and high speed to a manifold and then run a -8 or maybe a -10 return line back. The line from the tank to the filter and then to the pump is typically -12