What does tank mean in the tiling trade?

Tanking a shower area or bathroom means a method of water proofing an area or a room with either a paint on liquid or a water proof membrane. This is done prior to tiling. Your walls and floor are then water proof. So even if water got through the tiles or grout it would not penetrate the walls or floor.

Tanking is for sealing the walls from water ingress before tiling,you can get a complete tanking system from any tile outlet the price will about £55 upwards.