Even though our 5th wheel is a 2023, we got it used. It sat for a number of months with 'stuff' in the two black tanks which caused us some issues. We had a company called Kleen Tank pressure wash the inside of the tanks to get the clean and afterward they made some good recommendations. One of those recommendations was to flush each black tank with 8-10 gallons of water each time after dumping, then add 5 gallons of water to the tank. Instead of swapping hose connection each time we do this, we installed a manifold with integral ball valves that allows us to flush without disconnecting anything.
I created a video describing what we did. The link is below. Less than $200 and it works well.
https://youtu.be/JCaFXPbtY7c
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