depends on the type/brand


appropriate size connection to water supply can be anything from 3/8" to 1/2"
most dont require backflow prevention as they normally have an air-gap to storage tank

most have flexi hose drain which you will need to discharge to appropriate outfall, trapped if necessary - i normally hook them up using 1/2" hose barb bushed to 40dia fem iron connected to trap - you could do the same creating the trap if needed with some pressure pipe - there is usually some messing about with them....