Are you using on-board or city water. What is the PSI if using CIty water?
I know one park where the PSI is 120 PLUS!! That's enough to blow the ends off your water hose (it has happened) and blow past the seals in some toilet valves flooding everything.
A regulator can tame it.. Two ways to do it. IF it is a city pressure issue I would suggest a Valterra adjustable set to about 50 PSI or a Watts or Zurin "Whole House" likewise set to 50 PSI. these last two have a bell shaped Upper housing the pressure adjustment is the bolt that would attach a genuine bell to it's yoke or handle. NEW my ZUrin was tested from zero flow to full shower flow and the pressure never even wiggled.. 10 years old they need new parts and can be rebulit
OF you could splice (Cut actually) into the water line up the connections from whatever they are to 3/4 inch Garden Hose (One male one female) and put one of the el-cheapo cylinderical RV Pressure Regulators in the line, they will restrict flow too much for a shower but may provide enough to flush the flusher. i'd use a High Flow type first.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times