Feliz tres Reyes to you too.
There is no point in washing out a sinus, if there is nothing in it and just because people say that they have "sinusitis" is meaningless....amateurs.
Sinusitis is a blocked nose with thick coloured nasal discharge and an X-Ray showing the sinuses "full." Then and only then would i allow anyone washing out my sinuses.
Now washing your "nose " out is quite a different kettle of fish and this may be indicated for certain conditions which are not commonly met with.
So......Mr Sam has been advised perfectly as to the treatment of his condition and doesn't need his sinuses washing out.
As for you, or indeed anybody else, a cold could turn into sinusitis........but not as commonly as people would like to make out.