How odd! Mine have no roots at all. Only the dark red shoots, thought they were mould so was about to throw it out when luckily I realised they were little hard lumps.
I just dumped mine in a jar of water, it is sort of wedged in the top, so about two inches under water and the rest sticking out the top.
Surprisingly little rotting going on. Have changed the water several times. I might have removed any roots when I shaved the mould off the bottom.
Just counted I have ten little shoots, one is clearly becoming a leaf. Getting exited.
Realise that the chance of getting any sweet potatoes is about zero. I go on holiday in May and it becomes very difficult to get tenders to survive two weeks away. It probably would have been better to eat it in the first place.