To repair a small leak in an RV gray water tank, it's important to use a product compatible with the tank's plastic material—typically polyethylene or ABS. For a permanent solution and if you're comfortable with DIY repairs, a plastic welding kit will fuse the plastic together and create a robust seal. Alternatively, you can use a flexible sealant designed for RV holding tanks, such as Alpha Systems 1021 Self-Leveling Lap Sealant, which adheres well to these plastics and remains flexible after curing. Epoxy putty sticks like JB Weld WaterWeld or Hercules Plastic Tank Repair Kit are also effective and easy to apply for quick fixes. For best results, confirm your tank's plastic type before choosing a product. If you need help identifying the material or want a specific kit recommendation, provide the tank manufacturer or model information.