I think that they assume you'll have access from below to tighten up the clamps. FWIW, in the USA, that connection should be made with a banded (reinforced) connector (has a ss shield around the thin rubber seal), but that still leaves you with the same problem of how to tighten it down to seal things up. Not sure how you'd make the connection if you can't get access from below unless you had enough depth to use the coupler on the drain with a short stub of plastic pipe on the other end, then glue that short stub into a coupler to the rest of the plumbing below.
Assuming you're using the hydroban to make a surface membrane, if everything is working properly, there should be no water getting below it, so rusting lath isn't an issue. Have never seen SS lath, but there are a few companies that make a plastic one, if you're worried about it rusting (shouldn't be an issue).
Sorry, don't know much more about it. You might check and ask that question over at www.johnbridge.com, they have lots more tilers and tile pros over there than here.