The negative pressure at the input to the pump is going to be a function of the size and length of the suction line, other restrictions of flow in that line, and the flow rate. The same is true for the line coming out of The Liquidator to the suction line at the pump though the much narrower line means the flow rate will be much lower. Perhaps your suction line to the pool is very short and efficient. Partially closing the suction valve in the pump suction line will direct more flow from The Liquidator.
Raising the water level in The Liquidator will increase the pressure at the output point, but only by that height difference and you said that it was full already (I disagree with Jason on this -- I think there is benefit to the input side if the water level isn't already at its maximum height, but I don't think there is any benefit increasing the input beyond that). Raising The Liquidator as a complete unit, making it higher than the pump suction line, will add to the pressure difference, but I don't know if it's enough to increase your flow rate by what you need. Raising it by 1 foot increases the pressure by 1 foot. You might just put The Liquidator on something tall to see what happens (assuming your piping will reach).
Richard