Some 1/3 holding tank sensor lights will not go out because all of the water in the tank will not drain out. TankTechsRx is not going to resolve this issue. A problem for all manufacturers is what material is used to construct the tank. Stiff plastic tanks drain well and will not belly but they have a tendency to crack from road vibration. Softer plastic compound tanks allow the tank to flex and not crack but without proper supports they will belly out very quickly. The belly will grow with the weight of the sludge that cannot be emptied out. TankTechsRx will remedy some of the weight problem but cannot resolve the belly itself. We cannot make water flow up hill. If the bottom of the coach is covered and the tanks cannot be seen, there is an easy way to detect a belly in the tank. Pull the handle. If the water stops flowing very quickly with little dribbling, there is not much of a belly. If the tank dribbles for several minutes there is likely a belly. It drains slowly and continues to dribble because the weight in the tank is lessening and the plastic memory is returning the tank to a flatter position. There are some choices here. Brace up the bottom of the tank to take the belly out is the best permanent solution but it is not always practical or easily done. If done improperly holes can be rubbed into the tank from road vibrations causing the tank to leak. A simple fix is to climb under the RV and push up on the tank until it empties completely. Under NO CIRCUMSTANCES should you leave a public dump station with the valves open to allow the excess water to drain. That will likely bring about dirty stares and even possibly a very expensive pollution ticket. Remember it is going to leave a very long trail directly to you. With TankTechsRx in the holding tanks doing nothing is a viable option if it is not going to freeze solid. For freezing conditions get as much out as possible and add antifreeze to the tank for storage.