Jamieson, Fausset and Brown on Jeremiah 51:44

44. Bel ... swallowed--in allusion to the many sacrifices to the idol which its priests pretended it swallowed at night; or rather, the precious gifts taken from other nations and offered to it (which it is said to have "swallowed"; compare "devoured," "swallowed," Jr 51:34; Jr 50:17), which it should have to disgorge (compare Jr 51:13; Jr 50:37). Of these gifts were the vessels of Jehovah's temple in Jerusalem (2Ch 36:7; Da 1:2). The restoration of these, as foretold here, is recorded in Ezr 1:7-11.

flow--as a river; fitly depicting the influx of pilgrims of all "nations" to the idol.