How do I get from the zone that is underwater back to Orgrimmar?
Easiest and fastest way? Just use your Hearthstone.
Alternately, there are one or two above-water flightpoints from which you can hop on a windrider to Undercity or Grom'Gol and catch a Zeppelin from either of those. But they are phased, so you likely won't reach them until you've done several hours worth of quests in the zone.
Without doing any phasing/questing, sandy beach is available from the minute you enter the zone.
To get from Vashj'ir to Eastern Kingdom locations without a hearth:
- Go to The Clutch.
- Swim to the ocean surface.
- Look around for a nearby island (Sandy Beach) to swim/fly to.
- One side is Horde and one side is Alliance.
- Get flight path to all of Eastern Kingdoms locations.
There isn't an instant-return portal like there is for Deepholm or Twilight Highlands. You have to hearthstone or fly back.
You can also just wait for the next Tol Bard or Wintergrasp, after you are done with these BG's you will still be on the batllefield.
Fly to 13:48 get both flight masters (air and water).