The pipe and gravel field system has been around much longer than the plastic chamber systems and have been proven to work more efficiently.
Chambers can, theoretically, store a higher capacity of water. The chambers themselves can hold 3 or 4 times more water than the equivalent length of 4” pipe. However, the trench size for both products is the same – the pipe or chamber is laid in a 2’ wide trench and then covered with gravel. The trench for the chamber is completed with 1/3 the amount of gravel than the pipe system receives OR the pipe system has 3 times the amount of gravel of the chamber system. The gravel is the “filter” for the septic water that leaves the tank. More gravel equates to cleaner water being both absorbed into the soil and evaporated/transpired into the air.
Septic systems work best when they disperse the water over the largest area possible which is the fundamental operating principal of the pipe and gravel system. Chamber systems can store more water in the chambers, but this does not increase the absorption rate of the soil and, therefore, is no added benefit in most septic applications. Fields are not meant to store water, but to disperse water over the largest area available.
The best use for chambers is in small situations with excellent soil percolation rates. In clay or heavy soils, the water tends to sit in the chamber longer and this retention causes the growth of scum which can cause the system to fail sooner than a pipe and gravel system.