Grouting is extremely important for the end result of ceramic tiling in terms of both technical aspects and how well it looks. Grouting must be performed using materials specifically developed for that purpose, as defined and classified in the UNE EN 13888 standard.
Final cleaning of the work area is necessary so the tiles are correctly finished. So remove any leftover bits of cement, sealant and any other residue. Use mildly acidic descaling detergents to do this.
It is a good idea to impregnate the surface with clean water before any chemical treatment to prevent the cleaning agents used from being absorbed by the grout.
Do not use these kinds of products on recently installed tiles as the acid will react with adhesives and sealants that have not set yet.