ความคิดเห็นที่ 7 Example of a slow sand filter. 1) The concrete outer shell, built using 1/2 sack of cement mixed with 2 sacks of gravel and 1 1/2 sack of sand; 2) A length of PVC pipe, 15mm diameter; 3) A diffuser plate full of small holes, made from metal or pottery; 4) A 40cm layer of clean, washed, mediumgrade sand; 5) A 5cm layer of small gravel; 6) A 5cm ...