I am trying to follow what your procedure is. Black tank flush should be a seperate connection on the side of your RV than the clean water (city) connection. The valve manifold inside your garage is only for dealing with clean water and to my knowledge is not manifolded to the black tank flush.
Sanitize setting should be for sanitizing the fresh water system (hot and cold). Under this setting the pump should be sucking the sanitizing solution into the fresh water tank through the clear hose. If you have the water hose connected at this setting you may have blown a connection off the manifold. I would pull the panel and check the connections.
From manual on sanitizing:
How to sanitize
1. Level the motor home and drain the fresh
water system (see Draining the fresh
2. Prepare a chlorine solution using 1/4 cup
of household bleach (sodium hypochlorite
solution) to one gallon (3.785 liters) of
water in a container. Prepare one gallon
of solution for every 15 gallons of tank
capacity. This will result in a residual
chlorine concentration of 50 ppm in the
water system. If a 100 ppm concentration
is required as discussed in step 13, use ½
cup of household bleach with one gallon
of water to prepare the chlorine solution.
One gallon of the solution should be used
for each 15 gallons of tank capacity.
3. At the exterior utility center, place the
clear hose into the container with the
4. Turn the "city water / fresh tank fill valve"
to the FILL TANK position.
5. Turn the “sanitize / winterize intake valve"
to the SANI/WINT position.
6. Turn the “water heater bypass” (if so
equipped) to the BYPASS position. For
Aqua-Hot (if so equipped) please see the
Aqua-Hot manual for information.
7. Turn the water pump ON.
8. After the recommended amount of
solution is in the tank, turn the
"sanitize/winterize intake valve" back to
the NORMAL position.
9. Turn the "city water / fresh tank fill valve"
to the NORMAL position.
10. Turn the “water heater bypass” to the
11. Open the hot water line on all the faucets
(kitchen, lavatory, shower and outside
shower) until water begins to flow
continuously and a chlorine smell is
12. Close the hot water lines and repeat with
the cold water lines on the faucets.
13. Let the solution remain in the system for at
least four hours when disinfecting with 50
PPM residual chlorine. If a shorter time
period is desired, then a 100 PPM chlorine
concentration should be permitted to sit in
the system for at least one hour.
14. After the required period, drain the
chlorine solution from the fresh water
system (see Draining the fresh water
system). Some solution may remain in
the water heater and will be flushed in the
15. Fill the fresh water system using clean
(potable) water (see Fresh water
connections) completely full.
16. Then, drain the fresh water system (see
Draining the fresh water system).
NOTE: If a chlorine taste lingers in the
water, flush the water system with a
solution consisting of one-quart vinegar to
five gallons of clean water. Re-flush as