SHURFLO Mains Press Regulator, water inlet, Black, USA f-NPT-3/4, has a built in regulator helps protect water system from high pressure damage. (Pressure is reduced to a nominal 50 PSI.)

The Filter screen prevents dirt and foreign substance buildup
Built in check/non-return value, prevents water loss when pump is on
The water enters the inlet via a 3/4'' NPT USA female thread**. (A screw on protection cover is also included).
The fitting requires a hole in the wall of about 85mm diameter, and extends back around 80mm with a male 1/2 BSP thread for connecting RV pipework