What are the ongoing running costs?

There are three main costs to factor in:

• Electricity: Running costs equate to less than a 60-watt lightbulb running continuously – approximately £65 per year for an average domestic property

• Desludging: Every 2–3 years, similar to a standard septic tank emptying. You can use any licensed waste contractor, including the one you already use      

• Annual servicing: Required by law under the Environment Agency’s General Binding Rules. Typically around £150 + VAT per year.