Signs your tank is full
An overflowing cesspit or septic tank is a public-health problem and an expensive day. The good news: tanks rarely fail without warning. Below are the signs your system is at or near capacity, in roughly the order they tend to appear. Catching it at sign #1 means a normal slot. Catching it at sign #5 means an emergency callout.
Sign #1: Slow drains
The first sign of a near-full tank is usually drains that take longer to empty than they used to. The downstairs loo holds water for a beat too long. The kitchen sink takes a few seconds to start draining. Showers leave a small puddle.
This isn’t always the tank — partial drain blockages do the same — but if it’s happening across multiple fixtures at once, the tank is the more likely cause.
Sign #2: Gurgling
When you flush a toilet or empty a sink, you might hear a gurgle from another drain in the house — typically a shower or floor gully. That’s air being displaced by water in a system that’s lost some of its venting capacity, often because the tank is too full.
Sign #3: Smells outside
A working tank shouldn’t produce smells outside the tank. If you can smell sewage in the garden — particularly near the cover, or downwind of it — something is up. Either the tank is overflowing slightly through a vent that should be sealed, or the surrounding soil has reached saturation.
Inside the house, a slight sewage smell from a downstairs loo or utility-room drain often means the tank is full enough that gas is being pushed up the pipes.
Sign #4: Soft or soggy ground
Water-logged ground above or near the tank — particularly noticeable in summer when surrounding ground is dry — means liquid is escaping from the tank or its surrounds. For a septic tank, that often means the soakaway has failed and effluent is welling up; for a cesspit, it usually means the tank is overflowing through the cover or a seam.
This is a same-week problem. Don’t leave it.
Sign #5: Sewage in the house
The last warning sign is no longer a warning. Sewage backing up through the lowest drain in the house — usually a downstairs toilet or shower — means the tank has nowhere left to send waste, and gravity is doing the rest.
Stop using the system immediately. Don’t flush, run washing machines, or use showers. WhatsApp us with your postcode and we’ll get a tanker to you the same day. Emergency callout details.
Other signs (less obvious)
- The level alarm has tripped. Many modern cesspits and treatment plants have a level alarm. If yours has gone off, that’s usually about three days’ warning before sign #5.
- Lush, faster-growing grass over part of the soakaway. Effluent fertilises grass — patchy fast growth in winter, when the rest of the lawn is dormant, is a soakaway-failure tell.
- Drain flies in the kitchen or bathroom. Small persistent flies near drains often indicate a film of organic matter at the top of a near-full tank.
What to do at the first sign
Sign #1 or #2: WhatsApp us. We’ll book you in within the same week. The job costs the same as a routine empty, and you’ll save yourself the panic.
Sign #3 or #4: Call us. We’ll prioritise within the next 24–48 hours.
Sign #5: Call now. Same-day callout. Emergency callout.
Setting a schedule so this doesn’t happen
The best way to never see signs #2–#5 is a routine. Once we know your tank size and household, we set an interval and stick to it. You don’t need to remember anything — we WhatsApp before each visit. Cesspit households on a regular round rarely have a problem because we’re back before the tank gets close to full.
Last updated 2026-05-07. Written by the TankAway operator. We empty tanks for a living — this is the advice we’d give a friend.
FAQs
How can I tell if my tank is full before there’s a problem?
Slow drains, gurgling when you flush, and smells near the cover are the early signs. Sogginess over the tank, alarm trips, or sewage backing up indoors are the late signs — call immediately if you see any of those.
My tank alarm has gone off. Is that an emergency?
Treat it as urgent rather than emergency — you typically have 2–3 days before sewage backs up. WhatsApp us with your postcode and we’ll fit you in within 24–48 hours, same-day if it’s already overflowing.
Why is the grass over my soakaway growing faster?
Patchy fast-growing grass over a septic tank’s soakaway — particularly in winter when the rest of the lawn is dormant — usually means the soakaway is at capacity and partially treated effluent is fertilising the grass. Time to empty the tank and possibly investigate the soakaway.
Tank's full? TankAway.
Send us a photo of the cover and your postcode. Firm price within the hour.