Planned disposition of radioactive high-level waste (HLW) sludge contained in 177 underground tanks at the Hanford Site in Richland, Washington will involve immobilization of the HLW sludge in a glass matrix (i.e., waste vitrification) and subsequent storage in an underground geological repository. Before vitrification, the waste slurries are subjected to a number of pre-treatment operations, including 1) dewatering of retrieved tank waste slurries into a concentrated HLW stream and a low-activity waste (LAW) stream using cross-flow filtration and 2) chemical leaching and washing of the waste solids to remove materials that would otherwise limit the HLW loading in the glass matrix. Appropriate selection of pre-treatment conditions, specifically cross-flow filtration axial velocity, transmembrane pressure, and bounding dewatered solids concentrations, requires knowledge of the tank waste rheology and undissolved solids particle size distribution. Physical characterizations of Hanford tank wastes are limited, as the 177 underground tanks contain wastes from a variety of nuclear material enrichment, recovery, and reprocessing process streams. To better characterize how Hanford HLW waste will behave during the planned pre-treatment operations, the rheology and particle size distribution of actual Hanford tank wastes were studied as a function of treatment cycle in a bench-scale cross-flow filtration and leaching system. In this presentation, the methodology and measurement results for rheology and particle size of as-received and treated radioactive Hanford tank wastes will be outlined. Next, the influence of filtration and chemical pre-treatments on each will be discussed. Finally, a discussion of potential pre-treatment operational impacts will be given, focusing on aspects of cake formation, laminar-to-turbulent flow transitions in the filter system, and re-suspension of settled solids.