the picture is simple an example of an 'on/off' inline water valve - but what will work best in 'your' situation depends on your plumbing type - but most RV factories use 'pex' type lines(usually blue and red)...and with some standard 'flexible' water lines in other areas.
they make these water valves to fit most any type and style of plumbing you wish...
and, no, just 'fixing' the Anderson valve/cartridge over and over is also not a 'solution', as you assume, unless you like doing the same thing over and over. I find that the in-line cutoff valve actually creates a new option for filling the water tank, without having to 'wait' for it to fill while no other plumbing items can be used. This way I can do both at the same time, and no longer be concerned with the 'leaking' Anderson 4-way valve.
I also installed a water line cutoff behind my toilet, as cutting off the whole water system for a whole day while trying to diagnose and fix a leaky toilet is also aggravating.
It's interesting that in most every home there is a water line cutoff at every fixture, but in most RVs there is none, only the main cutoff.
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