Those indicators are notoriously inaccurate. As they age, the sensors collect debris on them and will often light despite there being a low liquid level in the tank. I just kind of know how long we can go before having to dump tanks, and only use the indicators as a rough guide. You can try filling your tank with water, or almost full add some cleaner, then drive on a rough road with lots of curves. That may help, at least temporarily. With the black tank, the drill is to fill it half or so, add lots of ice cubes, and drive for awhile. Again maybe a temporary fix.
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