Thank you all for the replies and advice.

Now, just to clarify the above. Once I have boarded at LGA, I will simply be geting off at IAD, walking to the RCC (if I so wish) and then walking 'unhindered'(ish) to the gate for the MAN flight ?. No 1hr+ queue through international security a la the MAN flight from ORD ??.

Sorry if I seem to be questioning anything above, but I find it amazing that leaving the US on an international flight can be so straightforward at the moment. Is IAD unique in any way for this ?.