99 C280 Gas Gauge Problem

[aklim]

My fuel gage is acting up. Before dinner, it registered 1/3 of a tank. Filled it up and turned it on. It registered empty. Turned car off and turned it on but no luck. Proceeded to drive it home. About 30 seconds later, the orange warning light came on to indicate low fuel. I believe the delay was some sort of anti-slosh thing. Went home (2 miles away), slut down and turned it on and all is well again. My understanding is that there are 2 fuel sensors in the tank because it is a hump style. Does anyone have the test procedure to figure out which one is bad or how do I get it? I doubt it is the gauge but is there an confirm test procedure? TIA