I. Project Background: Sewage Treatment Challenges in a Humid and Hot Environment In early 2025, a municipal sanitation department in a district of Guilin City (hereinafter referred to as 'the Client') discovered during routine inspections that sewage pipelines in multiple old residential communities and urban villages within its jurisdiction were frequently blocked during the rainy season, with some areas even experiencing sewage backflow. Mr. Li, the department’s head (a pseudonym), stated directly at a working meeting: 'We need equipment capable of maneuvering flexibly through narrow alleys while efficiently treating sewage—and it must be a blue-license-plate vehicle operable by drivers holding only a Class C driver’s license, thereby reducing labor costs.' Guilin is located in a subtropical zone, characterized by year-round high temperatures, abundant rainfall, and high humidity—posing stringent requirements on vehicle rust resistance and sealing component durability. Mr. Li emphasized: 'Traditional vacuum sewage trucks used in southern China often begin exhibiting bottom-tank corrosion after two or three years of operation, and sealing rings tend to age prematurely. This time, we must select a vehicle engineered to withstand humid and hot conditions.' II. Internal Vehicle Selection: From Requirements to Comparative Analysis The Client promptly established an internal procurement team led by Mr. Wang, Head of the Equipment Division. Based on publicly announced tender information and local procurement practices, the budget was capped at approximately RMB 226,000. The team initially shortlisted three candidate models: the Dongfeng D6 Blue-License-Plate Sewage Treatment Vehicle, the Foton Time Blue-License-Plate Vacuum Sewage Truck, and the Sinotruk HOWO Blue-License-Plate Vacuum Sewage Truck. After three rounds of deliberation, the team focused on the Dongfeng D6 chassis for the following reasons: Chassis Advantages: The Dongfeng D6 chassis enjoys high market penetration across southern China, supported by a dense network of service centers and affordable spare parts. According to MIIT announcement parameters (e.g., model CLW5070GSSD6), its chassis design is mature and well-suited for specialized vehicle conversions. Superstructure Configuration: Chengli Special Purpose Vehicle Co., Ltd. proposed a solution featuring a tank fabricated from high-strength steel plates, internally coated with a dual-layer anti-corrosion system to effectively resist sewage-induced corrosion. Sealing components utilize imported nitrile rubber—oil-resistant and highly durable—specifically optimized for humid and hot environments. Blue-License-Plate Advantages: The vehicle’s compact dimensions (approx. 5995 × 2000 × 2600 mm L×W×H) enable easy access to narrow alleys in historic urban districts; operation requires only a Class C driver’s license, significantly lowering staffing barriers. At an internal meeting, Mr. Wang remarked: 'Based on parameter comparisons provided by Chengli (e.g., model CLW5180GSSD6), the Dongfeng D6’s MIIT announcements are complete—ensuring nationwide registration, annual inspection, and commercial operation compliance. Moreover, Chengli sells directly from the factory, eliminating intermediaries; for identical configurations, this saves RMB 8,000–15,000 compared to 4S-channel procurement—a critical advantage given our tight budget.' III. On-Site Inspection of Chengli’s Manufacturing Facility: Verification of Rust Resistance and Sealing Performance To validate product performance under humid and hot conditions, Mr. Li led a delegation to Chengli Automobile Industrial Park in Suizhou, Hubei Province. The inspection focused on three key aspects: Rust-Proof Coating Process: Chengli engineers demonstrated the tank’s interior epoxy resin + polyurethane composite coating, with a thickness exceeding 500 microns, and conducted simulated salt-spray testing. Mr. Li commented: 'This coating far surpasses conventional anti-rust