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Dumping the tanks: when, in what order, what never goes in

This is how Forest River’s travel trailer and fifth wheel owner’s manual says to do it. Your own RV’s manual comes first: tank layouts and valves vary.

1. Wait until the black tank is 3/4 full

The manual says never dump the black water tank until it is 3/4 full, so there is enough water in the tank to flush the waste into the sewer line. If it isn’t, add water to the 3/4 mark before draining. After dumping, keep enough water in the black tank to cover the bottom, so residue doesn’t harden.

2. Black first, then gray

1. Connect the sewer hose to the RV outlet and to the dump station inlet. Make sure both ends are secure.
2. Drain the black tank first. Let it empty completely, then rinse it with several gallons of water through the toilet.
3. Drain the gray tank last: its soapy water rinses the drain line and the hose.
4. Close the valves, wash the hose with clean water, and cap both the RV outlet and the dump station inlet.

3. What never goes in

• Only waste, normal drain water and biodegradable RV toilet paper in the black tank. No wrappers, gum or cigarettes, however small.
• Use deodorizing and cleaning chemicals made for holding tanks.
• Never chlorine or caustic chemicals such as drain openers or laundry bleach, no household toilet or drain cleaners, and no automotive antifreeze.

The manual also says to empty both tanks before each leg of a trip, which cuts the weight you tow.

Source: Forest River travel trailer / fifth wheel owner’s manual, Section 5 Plumbing (Holding Tanks).