From your description, it sounds like it's a plaster trap.
I say you're correct, hospitals use them to keep plaster from casts out of the drain lines, dentists offices use them as well, .IMHO they seem like disposable solutions to a non forgiving substances and if you've ever had to pay a...
If the rebar is the concern just dip them in creosote to prevent the rust, then you're good to go.
Wouldn’t be the first time I heard someone say an inspector said or asked for something strange ;)
Hard to say exactly without actually seeing it but your plan sounds solid enough. Just attach a set of long supply lines to the sink and run the other ends (where they're easily accessible enough) to shutoff valves. You got this dude.
You're correct sir Bemis & Call never made tools specify for any railroad company but they did manufacture a lot of specialty tools for Ford Motor comp. for Ford Mechanics, back in those days not many people new what a car motor even looked like so to be a car mechanic was a good job to have...