How can I drain all the water in the ocean in minecraft?

I recently had an idea for a video I could make where I show what minecraft looks like when all the water was drained from the ocean. However doing it by normal means would take months to complete. Is there something I could do in mcedit or a command to get rid of all the water in the ocean?

This is the command you want:

/setblock ~ ~ ~ repeating_command_block{auto:1,Command:"execute at @p run fill ~-15 ~-15 ~-15 ~15 ~15 ~15 air replace water"}

This puts down a command block that constantly replaces water around you with air.

That's the answer to your question. But the solution for your problem is:

Create a customised world with the water level at the lowest possible value.