Even at a full-hookup campsite with a sewer connection, RVers should avoid leaving the black tank valve open continuously. The tank that holds toilet waste needs sufficient water to discharge its contents all at once. Having a hose connected does not automatically mean the valve should be left open.
When liquids drain first, emptying becomes harder
A September 16 maintenance tip from RVTravel recommends allowing the tank to fill to a certain level before emptying it. Jayco likewise explains in its Swift Li manual that using the tank with the valve left open can allow liquids to flow out first, leaving solids behind and potentially causing a clog.
The vehicle manual should determine when to empty the tank. RVTravel’s general guidance uses roughly two-thirds full, while the Jayco manual cited here uses about three-quarters full. Rather than applying one figure to every RV, it is important to confirm the procedure for your own model and waste-discharge system.
Empty the gray tank after the black tank
Under a typical gravity-drain procedure, empty the black tank first, followed by the gray tank, which collects household wastewater. Jayco’s manual advises this sequence so water from the gray tank can rinse the inside of the sewer hose. Close the valve after each tank has been emptied.
Before draining, level the RV and check the hose and its connections. Wastewater should go only to an approved sewer connection or designated dump station, and the hose should be cleaned before it is stored.
Vehicles with a macerator pump or a dedicated flushing system may have different operating sequences and precautions. If a tank does not empty properly, consult the troubleshooting procedures in the vehicle and equipment manuals rather than leaving the valve open or operating equipment arbitrarily.
Source: RVTravel’s September 16 RV maintenance tip · Jayco Swift Li official manual, sanitation systems section
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