Ask for a qualified surveyor or wastewater professional to inspect the tank, pipes, treatment system and percolation area before you commit to the purchase. They should look for signs of leaks, blockages, poor drainage, odours, structural damage and whether the system appears suitable for the property. Check with the seller or solicitor that the system is registered where required and ask for maintenance, desludging and repair records. Requirements and costs can vary, so discuss any concerns with your solicitor and check current guidance from the local authority or the Environmental Protection Agency.