"Septic system" covers several different setups, and which one a home has changes both the running cost and the questions to ask. Ontario groups them under Building Code Part 8 as Classes 1 to 5. The one most rural homes have is a Class 4: a conventional septic tank feeding a leaching bed. A Class 5 is a holding tank, a sealed vessel with no bed that simply stores everything until a truck empties it. Between the two sit advanced or aerobic treatment units, which pump air through the effluent to treat it further before it reaches a smaller or more sensitive bed.
Conventional Class 4 is cheapest to run; an aerobic or advanced unit adds $200 to $800 a year in required servicing; a Class 5 holding tank can cost $2,000 to $6,000+ a year to emptyAddress before purchasePlumbing
The quick answer
Which kind of septic system a home has decides what it costs to live with. A conventional tank-and-bed is cheapest: pump it every few years. A holding tank has no bed and must be trucked out constantly, up to $2,000 to $6,000+ a year. An aerobic or advanced unit adds $200 to $800 a year in required servicing. Ask which one you are buying, and get the matching records before you commit.
A conventional Class 4 system is the cheapest to live with: pump the tank every few years and keep the bed clear. A holding tank is the opposite, since every drop has to be trucked away, often every four to eight weeks, which can run $2,000 to $6,000 or more a year and never stops. Aerobic and advanced units cost more to install, usually $10,000 to $20,000, carry a mandatory service contract, and have mechanical parts that fail, so budget $200 to $800 a year in servicing and expect the aerator pump to need replacing every few years. A holding tank in particular often signals a lot that could not support a normal bed, which is worth understanding before you buy.
How to spot it
Ask the simple question first: is this a conventional bed, a holding tank, or an advanced treatment system? Tells include an electrical panel, control box, or alarm near the tank, which points to a pump or aerobic unit, a small yard with no room for a bed, or a service sticker on the tank. The use permit and any maintenance contract name the system type outright, so ask for both.
What it costs
Running cost is the real story. Conventional is cheapest. An aerobic or advanced unit adds $200 to $800 a year in required maintenance, plus roughly $200 to $600 whenever the aerator pump gives out. A holding tank is the most expensive to live with, at $2,000 to $6,000+ a year in pump-outs alone. Installing an advanced unit new is $10,000 to $20,000.
What to do
Find out the system type and get the matching records: the pumping schedule for a conventional system, the service contract and recent reports for an aerobic unit, the pump-out frequency for a holding tank. Price the ongoing cost into your budget, because an aerobic contract or a holding-tank truck bill is a real monthly number. If the home has an advanced system, confirm the contract is current and ask why the system was needed in the first place.
Education and triage, not a home inspection. Casaroo flags what kind of system a home appears to have and the running-cost questions it raises, a licensed septic professional confirms the type and its condition. We flag; we don't inspect.
Common questions
What are the types of septic system?
Ontario's Building Code groups them as Classes 1 to 5. Most rural homes have a Class 4, a conventional tank feeding a leaching bed. A Class 5 is a holding tank with no bed. Advanced or aerobic units sit between, treating the effluent further with air.
What is a holding tank and why does it matter?
It is a sealed tank with no leaching bed that stores all the sewage until a truck empties it, often every four to eight weeks. That can cost up to $2,000 to $6,000+ a year, and it often signals a lot that could not support a normal bed.
How much does an aerobic or advanced system cost to run?
Budget $200 to $800 a year for the required service contract, plus about $200 to $600 whenever the aerator pump needs replacing. Installing one new is $10,000 to $20,000.
How do I tell which system a home has?
Ask outright, and check for an electrical panel, control box, or alarm near the tank, which points to a pump or aerobic unit. The use permit and any maintenance contract name the system type.
Running and install costs vary by system and site; always confirm with a licensed septic professional.
Last reviewed 2026-07-14.
This guide is general education, not a home inspection and not advice for your specific property. Always
consult the appropriate licensed professional, and get a licensed home inspection before you remove conditions
or buy. Cost ranges are 2026 estimates that vary by region, size, and access; confirm specifics with a
qualified professional.