Slow moving drains are unsanitary, frustrating, and messy. Over time they will also develop into a complete blockage and a possible overflow. 

1. Scum Buildup

Soap and grease scum are the most common causes of slow drains. The slow down may only affect a single drain, such as the kitchen sink, or it can affect the whole house if the scum builds up in the main drain line. The scum is sticky, so it catches other debris as it washes by. This leads to a slowly developing clog that first reduces drainage before clogging up completely.

2. Biofilm Growth

Biofilm is a mixture of mold and bacteria. It feeds on the soap and grease scum in a drain. Growth can be quite quick but it rarely causes a complete blockage. Instead, the ability of the sink to drain simply slows down to a trickle over time. Maintaining a clean drain is the best remedy against biofilm formation. Kitchen sinks and the drains in your bathroom are the most susceptible to biofilm.

3. Tree Roots

If every drain in the home is emptying slowly then the problem is likely in the main drain line. The cause is often tree roots. The roots invade the drain as they seek out moisture and nutrients. This slowly clogs the drain pipe, leading to slow drains and periodic sewer backups. The roots must be cleaned out regularly and then treated to reduce the speed at which it grows back.

4. Obstructions

Obstructions are typically caused by flushing things down the toilet, such as hygiene items or diapers. Usually draining slows at first, but eventually the drain may clog completely. Vegetable peelings and items accidentally flushed down a drain can also lead to a partial obstruction. An obstruction may only affect one drain or it may affect the whole house, depending on where it becomes lodged. 

5. Clogged Vent Pipe

One component of the drain pipe system that is often overlooked is the drain vent pipe. Without a vent, a vacuum forms in the drain pipes and moisture can't drain away. Clogs usually form near the top of the vent, usually from outside debris that is introduced when the vent cap is knocked loose. Clogs can also sometimes form lower down if the drain ever overflows into the vent pipe, though. A plumber can locate and clear vent clogs. 

Contact a drain cleaning service if you are struggling with slow drains in your home.