It is important that wastewater does not back up into septic tanks or if effects the ventilation systems, interferes with wastewater flow and can cause scum layers to float up and flow out of the septic tank causing premature soil clogging. The general rule to apply is that if the ground level of the first absorption trench is higher than the bottom of the outlet pipe on the septic tank then a pump is going to be needed. The pipe also needs to have at least 1 in 100 fall to minimise risk of blockage. Wastewater introduced too low in the ground does not absorb into the rootzone and topsoil as effectively so it needs to be lifted up with a pump. It also means it can be transported further away from the building into higher, better drained and ventilated open ground with less shade and less chance of causing ventilation and other problems for the building. Pumps are also useful after septic tanks so that sand filters can be pressure and pulse dosed and the pumpwell, if made larger, can be used as storage to mitigate flows. "You can't push faecal material up hill" is a fact of life but there a plastic tipping buckets now on the market that may enable some sewerage pipes to just about be flat if there are ways greywater can be held back at a higher elevation to then flush solids though flatter sewers. If pumps can be left out of some marginal flat sites there would be financial savings up front and ongoing there might be considerable savings in maintenance and running costs. The legality of these systems in Australia still needs to be worked out but testing overseas suggests this technology might be able to make these savings.