When cutting very slowly in thick or thin materials, you need to be careful that you do not cut a hole through the floor of the tank. If you think this could happen, protect the floor by placing sacrificial layers of steel or scrap plate on the floor, making sure that there are no gaps where the stream could get between the scrap and cut the floor of the tank.

It is possible to cut a hole in the floor of the tank if you left the head on in one position and went to answer the phone and forgot about the waterjet. The jet is powerful enough that it will eventually cut a hole in anything in its way, including the floor of the tank. So always make sure you are thinking about how much energy is still available after going through the material you are cutting.