Beginner topic: Water
This holding tank takes "clean" water from a source such as a city or a well
These holding tanks temporarily stores waste water from activities such as dish washing and showering. This water is not suitable for drinking but is not strictly unsanitary.
This refers to sewage and waste generated by the toilet. This tank is often emptied first and grey water is used to flush it out.
Parts and accessories
Regulators are used to limit the water pressure sent to the RV. Many rv can only accept water pressure of low to moderate, because some parks water systems are large the pressure to maintain them may be high. This high pressure could damage the internal valves, pumps, or fittings. Simply turning the valve down will not lower the pressure. Valve limit flow, not pressure.
Filters can help to remove sediment and other particles in the water, most - if not all - water filters do not sanitise water. If the water being pumped into your RV is not already safe for consumption it should not be stored in your fresh water tank.