Before using the filter paper, the filter paper must be sprayed with water before it can be used. Because dry filter paper not only has poor filtering effect, but even when the sample volume is small, it will be sucked away by the filter paper, which will affect the experimental results. For different samples, students can use different sizes of funnels. Sometimes, if there are too many particles in the sample, we can use a funnel connected to the hose to increase the filtration speed. Sometimes there are too many samples, not only affecting the results of the experiment, but even filtering the samples is very difficult. At this time, consider changing another filter paper. When folding the filter paper, the more creases are better; because the sample contacts the filter paper, the area is relatively large, which increases the filtration efficiency. However, too many creases may damage the filter paper. Therefore, it is recommended to fold the filter paper into a “star” shape.