Background: I often enjoy building passages and tunnels under water, but once it is enclosed, the water doesn't recede since it was filled all the way. Currently, the only way for me to clear the water is to fill the entire passage with blocks and then dig them out.
Idea: Create pump blocks that will cause water to recede from enclosed spaces, even if it is fully submerged. Some provisions will need to occur so that this does not allow a player to accidentally drain the oceans. Perhaps each pump block has an effective radius upwards and to the sides?