This paper presents an alternative approach to extract the relative permittivity of dielectric materials utilising the waveguide method, by using fast-prototyped 3D printed waveguide standards. The standards have been fabricated by traditional 3D printing methods and were used to measure the relative permittivity of dielectric samples at C (4-6 GHz) and K-bands (18-20 GHz). The study evaluates standard laminates such as, FR4 and low-loss (e.g. Rogers) substrates, but also multiple 3D printed materials, comparing their dielectric properties against reference values from literature. Although measurement results obtained from several material samples show comparable relative permittivity values to those from existing literature, higher loss tangent values were observed. Such effect is sought to be associated to surface irregularities and interface mismatches of the printed waveguide standards. These findings underscore the potential of using 3D printing techniques for cost-effective dielectric property assessment while highlighting the need for careful consideration of anomalies in loss measurements.