This is your first tank – the solids tank – and this service is called a desludge. Pumpout frequency is based on local government regulations. If you only have one tank on your property, you require a desludge. After desludging your septic tank, you must add water to the tank as soon as possible (at least one third full) to prevent damage or lifting. Note that we will not do a desludge in or after heavy rain.