What is the inlet pressure of a condensate tank?

It can be at any pressure less than the main steam pressure.

I've operated steam systems with condensate tanks at widely varying pressures. The pressure a condensate tank, (which condenses some steam, but typically takes returns from steam traps) is wholly dependent on the system is installed in. Some heating system condensate tanks are designed to handle no more than 30 psig (minimum design requirement) yet take condensate at 1 or 2 psi from the steam traps. Other high pressure production lines operating at 50 - 100 psig could discharge to a tank at 50 - 100 psi, though the actual pressure would be reduced by the length of pipe transferring it to the tank. And the highest pressure I've operated a condensate system at was 600 psig, the steam system drew the steam for process from an extraction stage on the turbine at nominally 600 psi, though at low loads it was typically a much lower pressure.