4 pull handles = 4 tanks.
The two that are together(up front) are for the front shower/lavatory grey water tank and the toilet black water tank. (usually the front most pull is for the black tank
) To check which pull is for what tank(with all tanks empty), let your shower run for 5 minutes. Remove the drain cap and pull the rearmost of the two(slowly, pull only enough to let the water trickle out), to see if water runs out. This will be your grey tank.
The one at the rear of your trailer is for the rear bath black tank.
The one in the center is for the kitchen galley tank.