Move the RV to an outdoor area. Locate the damaged area on the tank. If the tank is empty, fill it with clean water before proceeding.
Put on safety glasses and disposable gloves. Use a cordless drill to drill a hole in each end of the crack to prevent it from becoming larger. If there is a hole larger in diameter than a quarter or if the crack is longer than a dollar bill, the tank cannot be repaired and must be replaced. Use sawdust to absorb any puddles that form.
Empty the tank by taking it to an appropriate dumping station. Wear gloves and use the proper tank hose assembly. Do not empty blackwater into a driveway or storm drain as it poses a hazard to human health.
With the rig parked outdoors, rough up the damaged area with coarse grade sandpaper. Brush or wipe away as much dirt and dust as possible. Wipe the area with a rag soaked in acetone. Dry with a clean rag.
Measure the damaged area and use scissors to cut a piece of fiberglass cloth that is larger than the damaged area by 1 inch in every direction.
Put on clean gloves and wear safety goggles. Remove the resin bag containing the tube from the Seal-N-Place kit. Keeping the bag sealed, break the tip off of the tube. Turn the key at the end of the tube to completely squeeze the tube's contents into the resin bag.
Combine the contents of the bag by squeezing and kneading it for a few seconds. Work quickly from this point on, the resin will harden completely in six minutes.
Open the bag. Generously apply the resin mixture to the damaged area and beyond using a craft brush. The resin should extend past the damaged area about an inch in all directions.
Cover the resin area with the fiberglass cloth, smoothing it down with a gloved hand to remove all bubbles, bumps and creases. Paint the entire piece of fiberglass cloth with the resin mixture; hold the cloth in place with one hand and paint it with the other. Taper the edges of the cloth by smoothing down to create professional looking finish. Allow the repair to dry completely.
