The Karlsruhe Tritium Neutrino (KATRIN) experiment aims to determine the effective neutrino mass with a sensitivity of 0.2$\,$eV/c$^2$ (90% C.L.) using the kinematics of electrons from the tritium beta-decay. In this thesis, the tritium retention of the KATRIN transport and pumping section is fully characterized. The neutral tritium flow has to be reduced by at least 14 orders of magnitude in order to sustain a sufficiently low background rate from the spectrometers. Therefore, dedicated vacuum simulations and commissioning measurements were performed. The results of this thesis demonstrate that the requirements for the tritium suppression are fulfilled.