To back and fill

Also found in: Idioms.
to manage the sails of a ship so that the wind strikes them alternately in front and behind, in order to keep the ship in the middle of a river or channel while the current or tide carries the vessel against the wind.
To take opposite positions alternately; to assert and deny.
to grow or become quite full; as, the channel of the river fills up with sand.

See also: Back, Back, Fill

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.