It does look like transit wax to me. As mz30 said, water will not remove it. Normally you will see some sort of pattern to the wax marks......like a cross or a couple of lines made with a wax marker or whatever they use. I once had a tile with a smiley face drawn on with wax! You will have to use whatever the shop recommends as if you buy your own then the shop could say you should have used ours and now we are not liable for any damage caused. Good luck.