How do you drain the fresh water tank without having to pump it all out into the grey water holding tank?

Disconnect clear water supply/hose. Turn on 12v pump. Turn on the sink faucets and open the grey water drain. Wait until the faucets start spitting water (you'll know).
Complete.
If you wish to split hairs yes there will be residual water left somewhat in the system but the tank will be emptied. Good luck and happy camping

I don't know what you will use, but when I am dry camping, my combined black and grey water tanks hold twice the fresh water tank capacity. SO: .... to fill it, I got a NEW 5 gallon yellow (diesel) plastic fuel tank('can') ..... (caution: do not put fuel into it), and used a drill pump (available for less than $8.00 from Harbor Freight) to pump fresh water from the 5 gallon 'can' into the fresh tank. repeat until filled. Since we live fulltime in a 5th wheel, I have my tools with me all the time.

buying a new, unused fuel container (5 gallon) , ensures no fuel contamination of your fresh water supply and tank. ALSO: get a NEW drill pump and do NOT use it for waste water or other fluids, keep in a small container for fresh water use ONLY..... recommend you let it dry thoroughly after each use.

The galley holding tank holds the grey water from the galley.

problem is there is an RV for your system. you will need to do the following.
Drain all holding tanks, fresh water and sewage

1. Attach garden hose to fresh water fill and fill tank.
2. Turn on pump switch and open cold water side of all faucet/ shower fixtures. Leave open until water runs clear. Repeat for hot water side.
3. Flush toilet until clear water runs into bowl.
4. Dump tanks again.
5. Sanitize water system. use a water sanitizer
6. If a water filter is installed, drain lines, remove filter assembly, clean and reinstall with new filter.
7. When ready to use the water heater, turn by-pass valve to open position to allow water to enter and fill the hot water heater tank.

The water tank drain should have a shut off valve to prevent water leak. I wouldn't cap it, you should want to drain water tank on occasion.

The RV sewer system should end in a 3", 31/2" or 4" black plastic fitting that has 2 to 4 plastic tabs that a flexible hose will lock on with a twist. The fitting probably has a cap twisted on. After the sewer drain hose is connected to the RV drain, and secured in the sewer, a 'T' handled pull rod should open the gate valve. Most drain the black tank first, then use the grey water tank to flush the hose clean. If the 'T' handles aren't in your sewer compartment, you'll have to look under the bottom edge of the RV to find them.

ok, been a while so lets ee if I can get this all down.

1 - Drain water from your holding tank and remove drain plug in hot water heater. Drain holding tanks ( Waste )
2- turn on bypass for hot water heater ( instruction if needed )
3 - Get yourself some winterizing fluid ( can't remember exact name ) from your local Dealer . 2 or 3 gallons should be good
4- Poor this fluid into your water rez tank. All of it
5 - now go around to EVERY tap in your trailer ( one at a time ) and turn on cold water until water runs pink ( or what ever colour fluid you bought ) Close faucet them do the same for hot water tap. Repeat this at every faucet. Even the ones outside if you have any.
6 Don't forget to flush toilet in water runs pink.
7. Ensure all gas vales have been turned off ( tank vales included )

If you did everything right you should be good to go.

Plz double this list to make sure I covered everything

U SHOULD HAVE A BLACK TANK AND A GRAY. TOWARDS THE BACK WERE U HOOK UP THE HOSE FOR DUMPING U WILL SEE TWO LEVERS ONE IS FOR BLACK ONE IS FOR GRAY. AND IF UR TALKING ABOUT FRESH HOLDING TANK LOOK UNDER NEATH AND U SHOULD SEE A PLASTIC NOSEL WITH A TURN VALVE LIKE WHAT BOX WINE HAS TO PURE A GLASS

If it is a big valve it is your sewer tank drain valve. There is two valves. One is the Black water drain and the other is the gray water drain. the black water drain comes from the toilet holding tank, and the gray water valve drains the shower and sink holding tank.

There should be a fresh water fill on the outside of the coach. If not then there is a valve that would need to be turned that will allow water to be put into the fresh water tank. If that is the case then it will be a bit more difficult to put bleach into the fresh water tank but not impossible. There will be a pump that draws fresh water out of the tank. You can disconnect the input and output lines. Connect the input line which comes from the fresh water tank to the output side of the pump. Then using a flexible line with a 1/2" pipe thread fitting, connect that to the input side of the pump. Put the loose end of the flexible line into a gallon of bleach and turn the pump on. It will draw the bleach out of the container and pump it into the fresh water holding tank. Now return the plumbing of the pump back to the original configuration. Using the valve system complete filling the fresh water tank with fresh water and allow to sit for a couple of days. Then open the low point drain on the fresh water tank and completely drain. When the coach is not in use make sure the tank is completely drained. There is also a fresh water treatment that you can purchase at your local rv parts department.