The method of reducing or eliminating a whirlpool forming above a strainer involves several techniques aimed at altering the flow dynamics around the strainer. Lowering the strainer can have the effect of moving it into a deeper portion of the water, which may reduce the turbulence that contributes to whirlpool formation. Similarly, raising the strainer might allow for a more stable flow, depending on the vessel's design and the water level.
Adding a floating object above the strainer can also help disrupt the surface tension and flow patterns, thereby minimizing the vortex effect that leads to whirlpool creation. The presence of such objects can break the flow of water in a way that stabilizes the inflow to the strainer.
The collective impact of these methods demonstrates that each can work independently or in combination to effectively manage the flow and prevent whirlpool formation. This holistic view on the problem supports the conclusion that all the described methods are valid approaches. Therefore, recognizing that any one of these changes can contribute to positive outcomes justifies the selection of the all-inclusive answer.