Be sure to use a dedicated hose for black tank flush, NOT your drinking water hose. That said, add a Y to the city water faucet & connect the black flush hose to the opposite side as your rv minus the regulator.
As to closing the black valve, you can close it without harm to the tank, but only for a few minutes with your full attention. Closing the valve for for few minutes to add more water will aid in removing more of the solids, but NEVER leave it unattended.
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Full-timed 10+ years
Sold '13 Redwood FB
Traded '13 GMC Denali DRW D/A
Replacement undetermined
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