I have a 2006 329RLS, it also came WITHOUT an anti-freeze inlet at the pump, which I did install, access to the pump, and hot water heater bypass valve is very difficult. I made access easier by making doors to the pump, and bypass valve:
My Winterizing Procedure(s)
1) Drain Hot Water Heater
2) Shift Valve to Bypass Hot Water Heater
3) Use Air Pressure to purge all lines of water
4) Use water pump to draw RV Anti-Freeze into system, opening the hot, and cold knobs on each faucet until anti-freeze runs out (don't forget the outside shower, low point drains, and toilet!)
5) With the water pump turned off, I then use a "Drill Pump" to pump RV Anti-Freeze into "City Water" inlet, again opening a faucet until Anti-Freeze flows, thereby protecting the inlet line.
6) Being overly cautious (as temps here in the winter can go as low -25F), I also purge the intake line from the fresh water tank, and use the drill pump to put some anti-freeze in it.
7) Any left over Anti-Freeze I dump in the drain traps (although when you open the faucets to let the anti-freeze flow what goes into the traps should be sufficient).
My Unit doesn't have the Black Water Flush, but I would use the Drill Pump to get it into the line
It sounds harder than it is, takes about 10 minutes, and 2 gallons of Anti-Freeze.
Good Luck
JP