diameter, the leak is said to be a stain. From ¾ to 1½ inches  in diameter, the leak is classified as a seep. Heavy seeps form  an area from 1½ inches to 4 inches in diameter. Running leaks  pool and actually drip from the aircraft. They may follow the  contour of the aircraft for a long distance.  made. Corrosion, such as that caused by water and microbes,  should be identified and treated at this time, even if it is not  the cause of the leak.  Rigid removable fuel tanks can be riveted, welded, or  soldered together. A leak can develop at any of these types of  seams or can be elsewhere on the tank. Generally, the repair  must match the construction in technique. Some metal fuel tanks experiencing minor seepage can be  repaired with a sloshing procedure. An approved sloshing  compound is poured into the tank, and the tank is moved  so that the compound coats the entire inner surface area of  the tank. Any excess compound is then poured out and the  compound in the tank is allowed to cure for a specified amount  of time. Minor gaps in the seams of the tank and repairs are  filled in this manner. The compound is fuel resistant once dry.  Check with the aircraft manufacturer to ensure that sloshing  is an airworthy repair for the aircraft fuel tank in question. Welded tank repairs are usually done by welding. These tanks  can be constructed from steel or weldable aluminum, such  as 3003S or 5052SO. The tank is removed from the aircraft  for the repair. It must be treated to remove any fuel vapors  that remain in the tank before it is welded. This is critical to  avoid serious injury from explosion should the fuel vapor  ignite. The manufacturer usually gives a procedure for doing  this. Some common methods for purging the tank include  steam cleaning, hot water purging, and inert gas purging.  14-47 Whether rigid removable, bladder-type, or integral, all fuel  tanks have the potential to develop leaks. Repair a tank  according to the manufacturer’s instructions. Some general  notes for repair of each tank type follow. Note that at the  time a tank is repaired, a thorough inspection should be  Remove the entire old gasket completely and clean all  mating surfaces. Clean surfaces and grooves allow a tight  seal. Inspect new gaskets and seals for any flaws. Follow  the manufacturer’s instructions for replacement, including  cleaning procedures and any sealing compound that you may  need to apply during replacement. Torque assembly bolts  evenly so as to provide even pressure and prevent pinching.  A leak can often be repaired by replacing a gasket or seal.  When this occurs, or a component is replaced or reassembled  after a maintenance operation, a new gasket, seal, or packing  must be installed. Do not use the old one(s). Always be sure  to use the correct replacement as identified by part number.  Also, most gaskets, seals, and packings have a limited shelf  life. They should be used only if they are within the service  life stamped on the package.  Fuel will usually flow in this  area along skin contour after  it is wiped dry Fuel usually drips at this point Size will vary with location and intensity Stain Seep Heavy seep Running leak $^{3}$/4" Max. $^{3}$/4" to 1$^{1}$/2"  1$^{1}$/2" to 4" Figure 14-89.  The surface area of collected fuel from a leak is used to classify the leak into the categories shown.  Replacement of Gaskets, Seals, and Packings Welded Tanks Fuel Tank Repair