Clear heavy-walled plastic hose should be stored aboard any vessel with a system that stores or moves fluid: fresh water, raw water, gray water, fuel, hydraulics, refrigerator compressor oil, the list goes on. I suggest that you carry both a 3-foot section of clear tube in every dimension to match the hoses on your boat along with 3-inch-long sections of copper tubing that match the inside diameters of the hoses. At some point, to diagnose a problem, you're going to want to watch the fluid going through a hose. Air pockets in raw-water intake lines and bubbles in a pressurized water system indicate blockages or leaks. Use the clear tubing to check the amount of diesel or water left in a tank by removing the inspection plate, pushing the tube to the bottom, then covering the top of he tube with your thumb. When you pull it up, the length of material held captive in the tube equals the depth of the contents of the tank. When filling an empty tank, I stop every 5 gallons, plunge my designated tank tube into the tank, then mark the height of the contents in the tube with a magic marker. Using this method, I always know my exact liquid reserves, give or take a gallon, while avoiding the chance of a misread gauge.