An adapter (20) includes an interface module (53) that receives signals from a first sensor (16,18) that indicate a first fill status of a holding tank (15). A control module (52) of the adapter (20) generates a control signal based on the first fill status. A toilet (12) is at least partially controlled by a toilet control module (52) that restricts a flush capability of the toilet based on the control signal. An isolation module (53) of the adapter isolates the interface module (53) and the control module (52) from at least one of voltage and current fluctuations that are external to the adapter.