Oil drain valve assembly removal on a Kawasaki FH641V-CS29-R engine (Husqvarna mower)

So, two days ago I loosened the drain valve screw (its made of rubber or plastic) and was able to drain some oil (I have too much oil in the crankcase).  I retightened the drain valve screw with a socket and I didn't over tighten it in my humble opinion, as I'm a weakling and I ususally don't overtighten things.  Now I can't get that drain valve screw to loosen.  It is shaped like a nut with a slot for a screwdriver also.  I"ve tried both a screwdriver and socket on it, but the socket just slips as the screw is rubber and is flexible.  Screwdriver doesn't work either, and the rubber screw is starting to tear.  I would like to take the whole assembly off and replace it, but can't figure out how to do that either.  The part that the drain screw actually screws into is also made of rubber/plastic and has an elbow coming off it where the oil actually comes out.  You cannot rotate this assembly much as the plastic elbow hits a piece of metal if you rotate it much and you can't go beyond that point.  Don't see how this can be unscrewed.  I'm no mechanic as you can probably tell.  Any help would be appreciated.  Not sure why these parts aren't metal, instead of plastic/rubber.  The diagram is on this website and is the "lubrication equipment" diagram.  I attached some pics.