D
DHTiling
Looked at these in B&Q the other day and it says on the packaging that the wax coating should be removed, and that the tile should be sealed prior to fixing and after grouting, which I would say is good practice with a porous tile.
Talk to your tiler.
They ain't really porous.. They stain because the polishing process opens up the surface pores and these are what collect the grout dirt etc and give that stained look, by sealing them you close these pores..
Porcelain on average is only 0.5% water absorbent and standard tiles can be +3% and well over.