Tanking economie

In AmE, "tanking" means failing, or hitting rock bottom. When a film tanks at the box office, it is a flop and has failed to generate enough ticket sales to cover its costs. If your football team was defeated 37-0, you'd say "the Lions completely tanked today." 

A tanking economy means the economy is down and folks are fearing a recession. When the economy is suffering, prices for real estate and such are very low. That is an opportunity for someone to purchase property, homes, office buildings, etc, at a below-market price. Eventually the economy will rebound (it always does) and that property will triple (or more) in price, making the investor a tidy profit.

verb (used without object)

7.

Slang. to do poorly or decline rapidly; fail: The movie tanked at the box office.

Source: http://www.usingenglish.com/forum/threads/76631-what-does-quot-tanking-quot-mean-in-quot-a-tanking-economy-quot