Ask three people in Sharjah what is under their villa and you will hear "septic tank", "sewage tank" and "the tank" for what may be the same thing. The terms are used loosely, and for the tanker that arrives it often does not matter. But the two types of tank fill differently, fail differently and need different maintenance, so it is worth knowing which you actually have.
What a septic tank is designed to do
A true septic tank is a treatment device, not just a container. Wastewater enters, solids settle to the bottom as sludge, grease and light material float as a scum layer, and the clarified liquid in between drains out through an outlet to a soakaway or drainage field, where it filters into the ground. Bacteria in the tank break down some of the solids over time. Because the liquid leaves, a septic tank fills slowly; what accumulates is mainly sludge, and the tank needs emptying when that sludge gets deep enough to reach the outlet.
What a sewage or holding tank is
A sewage tank — also called a holding tank — is sealed. Nothing drains away. Every litre of wastewater that enters stays until a tanker pumps it out, which is why these tanks fill far faster and why the collection interval is set by the household's water use rather than by sludge build-up. Many tanks in Sharjah that are called septic tanks are, in construction, sealed holding tanks, particularly where the ground or the plot does not allow a soakaway.
An underground tank is simply either of these, buried. The term describes where the tank is, not how it works.
How to tell which one you have
- How fast it fills. A sealed tank fills in proportion to your water use, typically within weeks. A working septic tank with a soakaway can go months between visits.
- The drawings. Building plans will show a soakaway or drainage field if there is one.
- What the driver sees. When the tank is emptied, a septic tank shows a distinct sludge layer and an outlet; a holding tank is simply full of liquid.
- Wet ground. Pooling around a septic tank often means the soakaway has failed and the tank is now behaving like a sealed one.
What each one needs
A holding tank needs regular emptying on an interval set by your water use, plus a proper cleaning when the sludge layer has built up enough to reduce its capacity. A septic tank needs less frequent emptying, but when it is emptied the sludge must actually be removed — pumping off the liquid and leaving the solids is what causes a septic tank to fail early. Both benefit from the same thing: being cleaned, not just pumped, so they keep their full capacity.
Our guide on signs your sewage tank needs cleaning covers how to tell the difference between a tank that needs emptying and one that needs cleaning.
What AL NISR DRAINAGE does for each
We empty and clean both types across Sharjah, and we take the contents to the Sharjah Municipality treatment plant in Al Sajaa. For villas and compounds, see our septic tank services. For holding, sewage and underground tanks at any property, see sewage tank cleaning. For the broader picture for homes and apartment buildings, our residential drainage page is the place to start. If you are not sure which you have, tell us when you call and the driver will confirm it on the first visit.