Lately a favorite of mine while describing the amount of small finishing work left on our house is
Death of/by a thousand cuts (UsingEnglish.com)
If something is suffering the death of a thousand cuts, or death by a thousand cuts, lots of small bad things are happening, none of which are fatal in themselves, but which add up to a slow and painful demise.
The phrase is a transliteration of the Chinese torture and execution practice Lingchi (Wikipedia):
a form of torture and execution used in China from roughly AD 900 until it was banned in 1905. It was also used in Vietnam. In this form of execution, a knife was used to methodically remove portions of the body over an extended period of time, eventually resulting in death.