Water system

[Southbourne]

Hi. This is a long shot. I have bought a 2002 Fendt caravan to be used static on a serviced pitch. I am a motor home owner so know a little about how things work. But this Fendt is very simple, no battery, no on board water etc. I think it has been tweaked a little over he years. It has taps with micro switches, and when taps turn on, 12v is applied to little external pump, and water pumps, but not from the taps... well not so well.
there are some unknown to me small plastic items, which have water flowing to them, but only seem to exit water through the floor. They have a screw on top, which you can tighten or slacken. There are a few, I think four, in various places. What are they for.
The pump pushes water ok, but should there not be a device which stops the water running out of the pipes and boiler and back into the water container?
Maybe I should update the water system generally, can I find a diagram of a simple but good arrangement anywhere.

 

[Damian]

Quote " there are some unknown to me small plastic items, which have water flowing to them, but only seem to exit water through the floor. They have a screw on top, which you can tighten or slacken."

These are drain points for the hot and cold water, tighten them down clockwise to close, opposite to open and drain.

Quote " should there not be a device which stops the water running out of the pipes and boiler and back into the water container?"

Yes there should be a non return valve just inside the van where the water comes in.