I have not seen a accumulator as a item listed as a option on any RV. I put on a 1 quart accumulator on my water pump when my RV was about 6 months old, it makes the pump very quiet, allows for some trickle of water use at night without starting the pump, and when you do trickle the water flow, the pump is on for about 4 seconds at a time, and will not sound like a marching band (like before without the accumulator).
Later I installed a 1 gallon water accumulator. It works very well, and I can use a lot of water between cycling the pump.
Fred.