More to the point, who is gonna sit there and just seal the grout lines; use a spray-able penetrating sealer, spray the grout lines,tile and all, let it seep in and then wipe it off with a lint free rag
I like miracle 511 myself
My work so nice! (cause I does it twice )
James, under the American industry standards your tile is either Porcelain or it's not. If it is, it has a water absorption of 0.5 percent or less. You're not gonna improve upon that without changing the appearance, as with Randy's epoxy recommendation.
You'll not have much moisture penetration through the tiles, but the tile is not waterproof.