This is often encountered for people who restore antiques, or who work in older buildings or on old machines. It may not be practical to replace a piece of crap, and polishing a turd may be all you can do.
Polishing A Turd is different from nigger-rigging because nigger-rigging is just to get something operational with little regard to how it looks or runs in the long term. Polishing A Turd involves making something look and operate as best as it can, although both may be major problems because it was a piece of crap to begin with. A Rolls Royce can be nigger-rigged, but you would not call it polishing a turd (unless it is a real ghetto cruiser). Putting new tires on a Yugo and filling its gas tank is polishing a turd.
My friend is polishing a turd - he's rebuilding the engine in his 1976 Vega.
The elevator was constantly breaking down in the last place I worked. It was old and beat up, and repairs were no better than polishing a turd.
"You're just polishing a turd fixing that Pinto."
"More like jack up the horn and stick a car under it!"