 of material for the box (glass company) 2. one (to start with) 24-in. long piece of tube, 4 in. in diameter (the tablets are 3-in. diameter) with cap 3. collar or gasket to join tube to box (toilet drain collar or flange) LOW-IMPACT SYSTEMS 4. 4-in. PVC pipe for inlet and outlet 5. plastic cement, gasket to seal top (weather strip), 4 clamps to secure top (automotive supply), drill, and keyhole saw 6. disinfectant test kit (swimming pool supply) Construction Glass is very hard to join properly. If you want to make a glass disinfection unit, start with an aquarium. Have a professional cut the inlet and outlet holes. Plexiglass can be cut with a hand saw or power saw, and glued with solvent such as xylene or a commercial cement. Drill a large number of holes or saw some slots in the bottom 4 in. of the dry feed tube, and cement the circle you cut out of the box top onto the bottom of the tube (Figure 7.15). When installing the dry feed tube in the box lid, do not fasten it permanently, for you may need to adjust its height later. Further, you may need a piece of scrap to place in front of the outlet port to adjust the internal liquid level. Operation and Maintenance Concentrated disinfectant can be extremely dangerous. Be sure to read the warning labels and handle the solid disinfectant and solu- tions carefully. Disinfectant concentration can be adjusted on dry feed units by changing the number of tablet reservoir tubes extend- ing into the waste stream, the depth of the tubes in the stream, and the concentration of the tablets. Disinfectant concentration is adjusted on liquid feed units by adjusting the concentration of the disinfectant solution being fed into the dosing or contact chamber and by adjusting the rate and length of time that the solution is fed. Liquid chlorine solutions are obtained by mixing granular high test hypochlorite with water to form a 2- to 5-mg/L concentration in the sand filter effluent (30 to 45 mg/L are required for septic tank effluent). The formula you need in order to calculate th