According to an old book that I have and from an internet source the right hand cylinder crosshead was connected to a feedwater pump behind the cylinder of 1.25" diameter which pumped water into the boiler. This is similar to the axle driven pumps on model locomotives for the same purpose,
Any excess water was sent back to the water tank by using a valve which allowed a controlled "leak. This can be adjusted to just supply the water required.
The hose from the tender water tank would only be under the pressure caused by the weight of water in the tank so a hose of Leather or some other material of the age could be used. There might have been a slight suction from the pump depending on the water level in the tender tank.
The valve chambers of the pump can be seen on my model Rocket below with the curved feed pipe above.
As to a Pressure Gauge if you look at the chimney of Rocket in a good photo you will see a "U" shaped tube attached to it . This looks like a Manometer which is a partial glass tube containing Mercury or other liquid which rises against atmospheric pressure to show the pressure in the boiler.
Hope this helps,
Colin.