How Often Should You Desludge a Septic Tank?

What affects the interval

• Number of people: more users fill the tank faster.
• Tank size: small or undersized tanks need emptying more often.
• Type of use: eateries, boarding houses, transient rooms and other commercial properties produce far more waste than a single household and usually need shorter intervals.
• What goes down the drain: cooking oil, grease, wipes and sanitary products build up quickly and are not broken down in the tank.

Why it matters

Solids settle at the bottom of the tank as sludge. Once the sludge level reaches the outlet, solids flow out with the liquid. That is when you start seeing backups, bad smells and wet ground near the tank, and when waste can reach groundwater and drainage canals. Emptying a tank on schedule is usually a single routine trip; dealing with an overflowing tank can mean extra loads, declogging and pipe repairs.

Local rules

Several cities in the Philippines have septage management ordinances that set a required desludging interval. Cagayan de Oro, for example, requires septic tanks to be desludged every five years. Rules differ by LGU, so check with your City or Municipal Environment and Natural Resources Office (CENRO/MENRO).

Keep a record

Note the date of each siphoning and keep the receipt. It tells you when the next one is due, and businesses may be asked for proof of desludging when renewing permits.