The invention discloses a three-cavity 
septic tank. According to the technical scheme, the three-cavity 
septic tank is characterized by mainly comprising a tank main body, the tank main body comprises an upper tank body and a lower tank body which can in 
butt joint with each other, the upper tank body and the lower tank body are both made of plastic through integral injection molding, two partition boards are arranged in the tank main body, the partition boards separates internal space defined by the upper tank body and the lower tank body into a first cavity, a second cavity and a third cavity which can allow 
water flow to sequentially pass through, main 
sewage inlets allowing 
sewage to enter are formed in the two sides of the upper tank body, the main 
sewage inlets communicate the first cavity with the outside, and each main sewage inlet is internally provided with a 
flange facilitating 
pipe placement. By means of the upper tank body and the lower tank body which are of plastic structures, cost of the whole 
septic tank can be greatly saved, the septic tank is convenient to process and can be produced in batches, and sufficient 
corrosion resistance is achieved. In practical application, openings can be formed in the side faces at multiple angles conveniently, and pipeline connection and laying are facilitated.