all, turbidity
渾 centers on a state of being mixed or undifferentiated: when everything is blended together, the result can be turbid or murky, and from that comes the sense of 'all' as an undivided whole.
渾 combines 氵 (water) with 軍, which likely contributes the sound. The idea of water mixed with sediment gives the turbidity sense, while the 'all' meaning may come from the notion of everything being stirred together.
Water 氵 mixed with an army 軍 of soldiers marching through a river stirs up mud, making the water turbid and blending everything into one murky whole.
For コン, imagine a con artist stirring up muddy water to hide the truth: con -> コン, and the turbid water conceals everything.