“Workers owning the means of production” isn’t some blanket cure-all statement that you can whip out to answer any problem.

I should have been more transparent in that I was referring to socialist examples such as China where 70% (paraphrasing, could be 60 or more) is owned by the state who services and provides for the proletariat. I didn't mean it as a generalized "cure-all" statement. There plenty of solutions for those problems though when you have a highly efficient, quickly-mobilized state workforce able to lay down railway lines, highways and hospitals in a matter of months. Your example with Cuba is working with the sanctions and how embargoed they are. I'm sure they would have the amenities of plumbing in each private flat in apartment blocks soviet-style if they could but climate and the embargo prevents them.

which produces up to 50% of its food from backyard and municipal horticulture. In places where they don’t have access to products that have embodied exploited labor, they need to take the proportional inputs seriously, instead of just assuring themselves that they’re cheap enough.

There's nothing stopping this from happening in large socialist economies either; Plenty of people garden and have this kind of horticulture in China and even capitalist economies, I know I do. I don't disagree with you on this. Larger horticulture and personal agricultural projects are important!

It means examining and ruthlessly criticizing all of the conveniences and abstractions that the capitalist world has created. For instance, asserting that to create “a reasonably healthy society” you don’t need piped water on tap within 15 steps in any residence

After living in a household with multiple people and struggling with my intestines for a while, I don't think having two bathrooms in a five-six person household with multiple women is a "luxury" or "abstraction". Nor are those things "luxuries" and "abstractions" for the elderly, disabled or those who genuinely need privacy because of conditions.

you definitely don’t need to mix your solid waste into black water and pump it into an underground tunnel network when a scoop of sawdust is enough to keep it sanitary until it becomes fertilizer in 6 months.

There is a reason we don't use human feces as fertilizer anymore. The bacteria in human feces as well as the level of nitrogen in it does not render it as a usable solution. It can work on smaller-scale, sure, but any form of economy of scale renders it unsanitary it is more efficient/cheaper to use other fertilizers than clean human feces of detrimental bacteria. In order to have a highly concentrated density of people, you definitely need sewers and plumbing. I do agree there are better solutions for grey-water storage, though and I get where you're coming from. I have family who have lived in a commune.

Also, plumbing isn't just used for waste solution. There is plenty of industry that needs plumbing. You do not want to mix the things that come from industry with black-water into wherever you are recycling the water.