Now, it's plumbing

With the help of a $.77 plastic pipe adapter and some creative reading of the user's manual, I can now suck water (and thus a bleach solution) up into the tank.

Thanks for all the help!

Rich

Usually "City Water" connection means for a hose. You use a drinking water-rated hose (usually white, maybe blue) connected to the supply via a pressure regulator then to the CW fitting on the coach.
"Gravity Fill" connection means a separate filler where you direct the stream of a hose into it to fill the tank. The male end of a hose (again DW-rated) will fit into that connector and there should be a vent plug to let air escape as water goes in. No need for a regulator to fill a tank with a GF.
Our first coach had CW and GW fittings. Present one has only the CW type and a valve to direct water into the fresh water tank.

For sanitizing I just use the gravity fill to the tank.

Um, newbie here. Does this mean simply pouring water and bleach into the "city water" connector?

The antifreeze connection is for winterizing. For sanitizing I just use the gravity fill to the tank. If you use either the antifreeze fill or the shore water connection and do not have the right vales open it will not make it into the tank you want to sterilize.
Were it me I would use a fairly strong bleach solution and let it sit for a day or two, pump through the system and rinse a couple of times then use some bicarbonate of sodium which will further help to clean and de-taste the system.

@CloudDriver -- thanks! I have the Owner's manual. and I'm following the instructions on page 27, which detail the procedure I outlined. The poorly-labelled picture in my blog is the "anti-freeze" connection, not the city water connection, which is a bit to the right and works fine. I'd lost the online link to the owner's manuals -- thanks! But I'm lucky enough to have a hard copy of the manual.

Rich

Here's a link to Coachmen Owners Manuals. Enter your model year (1999) and then select the link for the Class C motorhomes. Info on the plumbing system begins on page 26.

From a quick skim of the manual, it appears that your connection is for the city water inlet. It reads that there is valve to choose between either filling the on board water tank or to supply city water to the faucets, toilet, etc. from the city water hose. The water pump will only take water from the on board tank, so it will not work to suck a bleach solution into the piping. I have read on the forum that people pour bleach into their city water hose before connecting to the water source to get the bleach into the on board water tank. You want to sanitize the water tank as well as the piping, so filling the tank first, then pumping the dilute bleach through the piping from the tank is the way to go.