Ksp of Manganese Phosphate
Well, the MSDS entry tells me that the solubility is 50%. Converting, we get 0.5 g per gram of water, or 0.0005 g per liter of water. This is $s=1.4\times 10^{-6}$ moles per liter of water.

$K_{sp}=(3s)^3\times(2s)^2=6.14\times 10^{-27} \rm M^5 $