Is there a transit area or special line for transit passengers to avoid customs/immigration?

I'm coming from Newark, connecting on to Bangkok. We'll have to change terminals, and definitely want to squeeze in a shower between flights if we can. Will we have access to these areas if in transit?

Also, will we be asked to pay the int'l departure tax as well? The fee won't be included in our ticket, as we're flying space-available. Any tips are appreciated!