I'm trying to figure out how to best filter some liquids. A 5 gal bucket is filled with some filter medium (say sand on top 1/2 and fine charcoal on bottom 1/2). The liquid is slowly added at the top and gravity is used and vacuum may be used at some point with a complete seal along the bottom of the bucket. Now what I'm wondering is about the number and size of holes in the bottom of the bucket. I've done this with 2 smaller holes (diameter of a pencil) and there was a steady drip from each hole, about 1 a second. I used a different bucket and moved the holes from the extreme edges to 1/3 of the way from the edge so there were 2 holes directly across from each other - same size as before and another in the center and then 3 small slits about 1/2 inch long by 2mm across around the edges. This time flow was about 1/5 the rate as before. The reduction of flow was the opposite of what I was expecting and was wondering if there may be some reason for this which I didn't understand such as there being the same pressure in the vessel but spread out over more holes which would decrease the pressure at each hole. Since the surface of the filter material wants to hold onto the water, this decrease of pressure makes a big difference in flow. Is that a reasonable conclusion or am I experiencing something else I have to figure out.