How To Choose Between A Single Or Multiple Chambered Septic Tank

Posted on: 7 October 2015


A septic tank allows you to turn the most remote plot of land into a homestead the whole family can enjoy. When picking out your brand new septic system, you'll need to choose between a simple one chamber tank or a unit with two or more separate spaces. Figure out which design best fits your budgets and plans so you don't need to get a new tank within the first few years of moving onto your property.

Solid Settling

The number of chambers in a septic tank has the biggest effect on how well the solid waste in the tank settles at the bottom instead of flushing out into the drain line and clogging it. Without proper settling, you'll end up a clogged system that sends sewage backing up into the house. Two or more chambers cause solid waste to end up in the first chamber, while the water waiting in the second and third spaces gives smaller particles a chance to settle out too.

If the chambers are separated properly, the sludge at the bottom won't wash into the other chambers as easily either. A dividing wall along the bottom forces only the water at the top to spill over into the next part of the tank.

Cleaning Schedule

The biggest maintenance task for owning a septic tank is the pumping process. No matter what type of tank you choose, you must get it pumped at least once every few years or it could end up cracked and in need of replacement. Since multiple compartments help you gather solid waste at a higher rate, you need to get that chamber cleaned out more regularly. The small divided chambers also fill up faster. However, even the biggest single chambered tank eventually needs a complete pump out to keep working properly.

Soil Accommodation

What kind of restrictions is the local health department putting on your septic tank due to the soil conditions? Slow drainage and high water tables make it unsafe to use the usual standard tanks with open drain fields. Two, three, and four compartment designs allow for the extra space needed to accommodate alternative septic systems like,

  • Solid waste grinding pumps that save space in the bottom of the holding tank
  • Aerobic digestion systems that rely on oxygen to break down waste faster
  • Baffles and filters that keep solid and thick liquid waste from draining out into the field
  • Dosage chambers for systems based around bacteria additives that do the hard work of neutralizing your waste.

Water Velocity

Each flush or sudden drainage of the washing machine sends a jet of water shooting into the water holding tank. Sudden movement stirs up all the particles and solid waste trying to settle safely at the bottom of the system. Two-chambered designs can slow down the velocity of water entering the septic system by putting baffles and walls around the inlet area. Most single chamber designs feature the same basic water slowing baffles too now, so the two types of tanks don't differ too much in this respect.

Chamber Proportions

The only proportion important in single chamber designs is the overall size. If there's a second chamber added on, the first holding space should account for two-thirds of the total volume. This allows you to accumulate plenty of waste before any clogs develop and spreads the pumping visits as far apart as possible.

Talk to the septic tank installers to get a custom recommendation on which type of design to choose. Most installers charge by the size of the tank and not what's inside it, so choosing one with multiple compartments shouldn't increase your installation costs.

For more information, talk  to a company like Rob's Septic Tanks Inc.