Septic / Drain Field Issues

[WVBill]

So you are saying the drawing is “maybe” 100mm off?
And if that drawing (with unknown distance to tank bottom) were to be followed it would “quickly” clog because of that approximate 100mm difference?

Realizing now that the tank bottom is not shown - the drawing is probably correct if there is sufficient depth in the tank to allow for sludge build up. The depth from the bottom of the outlet elbow to the bottom of the tank basically determines how often you need to pump the tank.