Are you lot serious? @_@ Just make a SINGLE particle of PUMP and make it -255 temp. Problem solved.
The Issue however, is that TPT doesn't handle powder movement the same way Earth Editor or Powder Game does. Water moves according to an algorithm designed for making it level out like pools do IRL, and causes it to behave strangely in radial gravity mode.
...You don't even need to code this in. Just press W one time in-game to enable radial gravity mode. -_-
At any rate, due to the differences between TPT and Earth Editor, a black hole element that shifts gravity in such a literal form isn't likely to exist. Even when it does, without changing the way particles behave in TPT fundamentally, making even spheres will be difficult, and using liquids impossible.