There are 4 main causes of blocked drains: 1. Putting inappropriate items down sinks and toilets within the house. This includes food waste, fats and wipes. Apart from the obvious, the only thing you really ought to putting down toilets is toilet tissue and please bear in mind that fats can solidify in the pipes. 2. External items getting into the drains outside. The obvious items being leaves and garden debris. 3. Tree roots. These can cause damage to pipes underground if they grow too big and disturb the pipes. 4. Pipe structural issues. Joints can perish causing the pipe to drop or they can become squashed or distorted. See what you can do about these issues here