This paper presents the state-of-the-art in polymer-based 3-D printing of metal-pipe rectangular waveguides (MPRWGs) with the first reported terahertz filters, all operating within the WR-2.2 band (325 to 500 GHz): a 5 mm-long thru line, two 399 GHz single-cavity resonators and two 403 GHz bandpass filters (BPFs). Our thru line exhibits a measured average insertion loss of only 0.9 dB, with a worst-case return loss of 13.3 dB, across the band. The single-cavity resonators, without and with corner rounding compensation (CRC) are investigated with the use of an RLC equivalent circuit model. The uncompensated resonator exhibits a 2.3% frequency downshift and an increase of 10.8 GHz in its 3 dB bandwidth. The compensated resonator exhibits a 2.2% frequency upshift and an increase of only 2.2 GHz in its 3 dB bandwidth; clearly demonstrating that CRC helps to mitigate against increased coupling into the resonators, as a result of manufacturing limitations with low-cost 3-D printing. Finally, the 3 rd order Butterworth and Chebyshev MPRWG BPFs both have a measured passband insertion loss of only 1.0 dB. The Butterworth filter exhibits a 0.8% passband frequency upshift and worst-case return loss of 16.6 dB; while the Chebyshev filter exhibits a 1.2% passband frequency downshift and worst-case return loss of 10.4 dB. With our low-cost polymer-based 3-D printing technology, we have demonstrated measured performances that are better than those using metal-based 3-D printing in the WR-2.2 band and this may, in the not too distant future, challenge components manufactured using traditional machining technologies.