You will find all you need.
There are even photos that show why the "empty" light is always on and why the 1/3 light is a "not empty" light.
Deck angle will turn on the 1/3 light as water held by crud on the walls drains to the bottom of the tank and turns on the "not empty" light.
Black Tank 1 pictures from travel photos on webshots
The "Empty" light is actually a "Power On" light.
The bottom stud is the "not empty" light.
The middle one is the "Half Full" light
and the top one is the "Dump me soon" light
NEVER dump until the Dump Me Soon light is on.
If you MUST dump before then, flush toilet until the "Dump Me" light is on and then dump. This will make sure all solids have enough water movement to move them. After dumping, flush if you have a turbo flush or a flush cap. Then add the chemicals (2 Capfuls Calgon and your odor control chemical) and follow with a MINIMUM of 2 gallons of water.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW