How to Excavate a Septic Tank for a Mobile Toilet

The excavation of a septic tank for a mobile toilet involves steps such as site selection, size design, bottom treatment, compartment separation, and emphasizes anti-seepage, odor control, and safety measures. The specific operations are as follows:

1. Site Selection and Positioning

1. Terrain Requirements: Choose an area with higher elevation and smooth drainage to avoid low-lying areas prone to water accumulation, preventing rainwater backflow or sewage overflow.
2. Safety Distance: The septic tank should be approximately 1.5 meters away from the main body of the mobile toilet and kept away from drinking water sources and underground pipelines (such as gas and power lines). Before construction, contact relevant departments to investigate the distribution of underground facilities.

2. Excavation Size Design

1. Depth: Adjust according to the model. For ordinary cesspits, a depth of 1.5-2 meters is recommended. The excavation depth for the septic tank of a mobile toilet in Anyang is about 1.2 meters.
2. Diameter/Width: It should be 20 centimeters larger than the main body of the septic tank to ensure installation space. For multi-compartment septic tanks (such as three-compartment ones), the recommended width ratio for each compartment is 50%, 25%, and 25%, with a typical volume ratio of 2:1:1.

3. Bottom and Pit Wall Treatment

1. Bottom Anti-Seepage: Lay 10-15 centimeters of gravel and level it with concrete, or use a 10-centimeter-thick sand and gravel bedding layer and compact it. The bottom should have a slope (1-2%) to facilitate the flow of feces to the outlet.
2. Pit Wall Reinforcement: Keep it vertical and flat. Use bricks, soil blocks, or cement mortar plastering (2-3 centimeters thick) to prevent collapse. Alternatively, lay a PE anti-seepage membrane to enhance sealing.

4. Special Requirements for Multi-Compartment Septic Tanks

1. Installation of Fecal Discharge Pipes: Reserve fecal discharge pipes with a diameter of 10-15 centimeters between compartments, with a slope of 1-2% to ensure smooth fecal flow.
2. Odor Control and Sealing: Install anti-backflow valves at pipe connections. Use precast concrete slabs (8-10 centimeters thick) or brickwork for the cover plates, leaving a fecal cleaning opening (30-40 centimeters in diameter) with a lock, and raise it 5-10 centimeters above the ground to prevent rainwater from entering.

5. Installation and Backfilling

1. Placement of the Septic Tank: Use a level to calibrate the height of the inlet and outlet pipes to be consistent with the ground pipes. After fixation, protect the pipe direction with concrete or bricks.
2. Layered Backfilling: First, backfill sand and gravel to 5 centimeters above the pipes, and then compact it layer by layer with yellow soil to avoid settlement.

6. Safety and Maintenance

1. Safe Operation: Non-professionals are prohibited from working in the tank. When cleaning, wear gas masks and protective clothing, and prohibit open flames.
2. Regular Maintenance: Check the pipe sealing every quarter and clean the sediment. Clean 90% of the first compartment, 75% of the second compartment, and all the hard surfaces of the third compartment every year.

Summary: The excavation should strictly follow design specifications, incorporating anti-seepage, odor control, and safety measures, referring to the installation specifications for mobile toilets in Anyang (such as a depth of 1.2 meters and a sand and gravel bedding layer) or the design ratios for multi-compartment septic tanks (such as 50%-25%-25%).