Hoses for engine, accessory and emission systems are made of rubber and plastics that tend to wear out and harden when exposed to high heat under the hood and hence require regular check up for cracks, loose clamps, material hardening and leakage. Most hoses have clamps on them, which should be tightened to prevent leakage; if there are no clamps it should be ensured that the hose has not swollen at the fitting or has become rigid. To cut down the emission of hydrocarbons, the gases produced by crankcase blow-by are drawn through the PCV hoses and discharged at the intake manifold to mix with the fresh incoming air for combust. PCV hoses to be checked for cracks and then if blocked, should be cleaned with the help of solvent. These hoses, which usually come in colours, need certain thickness of the wall and certain temperature resistance; when replacing, make certain that the new hoses are made from the same material as the old ones. Hoses sometimes need to be disconnected for checking and identifying them helps in fixing them back in the correct manner. Some of the things that should be included in the inspection process of the T-fittings include whether the plastic has cracks or distortion which is likely to lead to leak. A small piece of vacuum hose can be used as a stethoscope to diagnose faulty vacuum hoses by putting this check probe up to your mouth and hearing, or rather listening to hissing. Fuel lines are usually connected under pressure and as such, if you need to remove the fuel lines be ready to mop the floor because fuel will drip. Look for signs of deterioration of flexible fuel lines particularly in regions of bends and fittings and when replacing it, only use hoses suitable for the particular fuel injection system. Some fuel lines have clips that allow the usage of easy to disconnect equipment on the fuel line. The metal lines used for the fuel lines under the body should be checked for bends, crimps or crack lines. If the fuel line is a metal type, it has to be replaced with the steel tubing, while copper and aluminum do not possess the necessary for resisting the vibrations of the engine. Moreover, check metal brake lines at the master cylinder and brake proportioning unit for crack, and loose fittings because if any spot of leakage is observed in brake fluid, then it means the brake system requires inspection.