1
general::
Waste more money in hopes of recouping previous losses, as in Hiring him to improve that software is throwing good money after bad; it's based on an older operating system and will soon be obsolete. [Late 1800s]
American Heritage Idioms
2
general::
Phrase(s): throw good money after bad
Fig. to waste additional money after wasting money once. • I bought a used car and then had to spend $300 on repairs. That was throwing good money after bad. • The Browns are always throwing good money after bad. They bought an acre of land that turned out to be swamp, and then had to pay to have it filled in.
McGrawhill's American Idioms And Phrasal Verbs