Citroen Xsara Picasso 2.0 hdi 2001 - coolant system bleed - pn1973

how do you know if the coolant system is blead correctly ? the heater is blowing hot and the bleed valve at the back of the engine has a little water coming out of it when you remove the screw but the valve near the thermostat has no water coming out except if you squeeze the pipe? i belive the the system takes 5.8 lires is this correct?