most of the cause jelling of the soilds then when you have flux of incoming water the jelled ball follows the water out in to the drian field yes the tank is cleaner but then your drain field ends up being replaced due to plugged soils. there are many states that will not let you use these items...
after ten years of sales in precast manholes it sounds like your installor did not install conseal in between cyc.and cones or adjustment rings or he did not jack the boots with boot jack hyd to the pressure the boot manufacture requires, in the manhole to the right spec or he did not tighten...
