The toilet bowl is a standard commercial toilet that would be used in a home, which means your trailer water system mimics that in your house. You trailer water system is pressurized at and from the hook up point, the garden hose. One difference from a home system is the anti-siphon valve just above the toilet flush handle that prevents water from below the valve from being drawn back up into the water system, thus preventing contamination of your potable water supply.
Your '57 trailer never had its own self-contained, self-pressurized water system. If you want such a system, you will have to buy all new components. Hope this helps.
Fred Coldwell, WBCCI #1510, AIR #2675
Denver, Colorado - WBCCI Unit 24
Airstream Life "Old Aluminum"
Airstream Life "From the Archives"