The waste being diluted enough so it’s able to be treated and doesn’t solidify or clog in pipes is something that I am sure is an actual issue. I wonder if they have to add water sometimes to offset the water saving of residents who achieve amazing low water consumption patterns? Also, if they have to add water to be able to actually process the wastewater as it’s received? This is why I think a way to create little bags of faeces like in the martian movie and book, makes sense. The faeces is a high cost, high value component. Simply bagging it means suddenly pipes have less physical material to address, and also, the faeces isn’t contaminated with other chemicals such as detergents or hair or clothes or or teeth or hand washing compounds.