Do I need a condendate tank

no you don't need a condensate tank.

you do however need another contractor..that pipe will never drain if it turns up and forms a water seal in the pipe. The radiator will need to be repiped..this should have been tested during the rough in..radiators get roughed in and OPERATED during rough in to prove to all parties involved that the piping is correct and that they operate. They then get removed and set aside for the rest of construction..this way everyone knows when the work was done the radiators worked. If the carpenters or others step on pipes and change pitches its then on them to pay for the correction..thats why we always prove operation.

NO, you don't need a condensate tank, and your piping won't work!

Early vapor systems usually had a return device or other mechanical devices that would kick into action if the pressure got up to the point that gravity could not return the condensate to the boiler.  Those devices are no longer manufactured. 

The general assumption of many contractors and engineers who really don't understand how the old vapor systems operated is that, 1.  The pressure of the system is going to go up to 2 psi.   and if the pressure is going to be allowed to climb to 2 psi, which will prevent gravity return, the solution is, 2.  a condensate return pump and tank set.



Of course, the more cost effective solution is to install a vapor stat that limits the pressure to 8 - 12 oz of pressure so that the gravity return can happen on its own.  This device is much less expensive than a condensate return pump, and it does not require ongoing maintenance expense.  Furthermore, the system will operate less expensively at lower pressures.



The solution is simple and straightforward, and for the most part is not part of the knowledge base of the current generation of hvac engineers and contractors.



As for your piping.  At first, when reading the verbal description of the problem, I was sympathetic to the contractor because I thought that perhaps his experience was in hot water and he did not understand the subtle differences.  However, when seeing the pics that you posted on this thread on the main wall, I can categorically state that the piping for this radiator, if it was a hot water system would not circulate because he created air traps without the ability to vent out the air pockets.  But it's not water, it's steam.  And as a steam system, it will not work, because he created a trap situation that both the steam line and the return line will not drain, and therefore this radiator will remain stone cold, regardless of what else is going on in the system.  I hope there is a way to correct the piping, because it will never work. 



The ability to thread 2 iron pipes together without getting the threads crossed does not make a contractor qualified to pipe steam or hot water heating systems.