1) Clear 2) Clear a clog 3) Clear a drain 4) Clear of clogs 5) Clear the drain 6) Clear up a clog 7) Open 8) Pull a cork out of 9) Pull the plug 10) Remove a clog from 11) Remove a plug 12) Remove the cap 13) To free from any obstruction 14) Use a plunger 1) Open 
• (v. t.) To free from any obstruction; to open. • (v. t.) To take the stopple or stopper from; as, to unstop a bottle or a cask.
to remove the stopper from: to unstop a bottle. · to free from any obstruction; open: to unstop a sewer. · to draw out the stops of (an organ).