If this is the case then the problem likely lies with your soakaway, not the septic tank. Every septic tank has a soakaway connected To It. A soakaway allows the liquid from the septic tank to drain away into the soil.
How quickly the septic tank soakaway becomes a failure depends on a few different things, including how often the septic tank has been emptied, the nature of the soil, the height of the winter water table, heavy rain periods and the deterioration of the septic tank itself.
People often make the mistake that when a problem develops with their sewage system it is the septic tank. But in most cases it is the soakaway that is the problem. The soakaway is a very important part of your septic tank sewage system. Over time all soakaways eventually become blocked as they silt up with sludge, grease and fat.
The solution is often simply having you soakaway pipes jetted to clear them and then ensuring you undertake regular maintenance and emptying.