Rusted or clogged manifolds

Hi,

Just bough a 2004 Centurion with a mercuriser 350. The buyer winterized it before delivery, and some hoses where unplugged.

I noticed that down on each manifolds, the drain hole was full of small chips of what appears to me to be rust or maybe calcium deposits, i' not sure.

I'm worried this could cause the whole system to be clogged.

Any hint if this is ''normal'' or if something need to be done? Removing those chips is enough?

Thanks