Abstract: A sensing system for sensing the level of liquid in a container and for providing an indication of the pressure within the container includes a magnetic member arranged for movement relative to a pneumatic switch operated by the presence or absence of a magnetic field. Spring means act on the magnetic member and urge it towards a first operative position. A weight is suspended from the magnetic member and the weight is positioned, in use, within the liquid in the container such that, when the level of liquid in the container falls to a predetermined level, the magnetic member is caused to move from its first operative position into a second operative position. The system further includes a manually displaceable member that is movable against the action of the pressure within the container and is movable by the pressure within the container when the pressure within the container exceeds a predetermined value.