Septic Tanks
HERMEQ septic tanks are blow moulded in high-density polyethylene, which makes them lightweight to handle into the excavation and resistant to corrosion from the surrounding soil. The rounded body makes the tank straightforward to install, and the super low profile keeps the dig shallow on sites where a deep hole is impractical.
The range covers three sizes of the Tricel Vento for homes and buildings that drain to the ground because no mains sewer is within reach. Every tank is available to buy online with nationwide delivery.
Low profile plastic septic tanks
The range is built around the Tricel Vento super low profile septic tank, a tank for properties that treat their own wastewater on the plot.
Polyethylene is far lighter to move into the dig than the brick and concrete tanks many installations are replacing, and it does not corrode in the ground, which is the usual way those older tanks fail.
The low profile shape is the main reason to choose this tank. A shallow body needs a shallower excavation, so it suits sites with a high water table, where a deep hole fills with water as it is dug, and sites with rock close to the surface. It is also the practical choice on tight plots where neighbouring foundations, buried services or restricted access for a large excavator rule out a deep dig.
Septic tank, cesspit or treatment plant
The choice between these three systems turns on where the liquid can go once it leaves the tank. A septic tank settles and partly treats the sewage, then discharges the effluent into the ground through a drainage field, so it is the right system where the soil drains well and the plot has room for the field.
A cesspit, also called a cesspool, cess tank or holding tank, is a sealed sewage storage tank with no outlet. Everything that enters it stays there until a tanker empties it, so emptying is far more frequent than with a septic tank. It is the answer where the ground will not take a drainage field and there is no permitted outlet for treated water.
A sewage treatment plant treats wastewater to a much higher standard and is the choice where the only outlet is a ditch, stream or other watercourse. The rules on small sewage discharges do not allow septic tank effluent to go straight to surface water, so on those sites a treatment plant takes the place of the septic tank.
Septic tank sizes
A septic tank is sized by the number of people using the drainage it serves, since that sets how much wastewater arrives each day and how long it stays in the tank to settle. Shared drainage, holiday lets, small developments and buildings that fill up at weekends or in season need more capacity than the bedroom count alone suggests, because the tank has to cope with its busiest days as well as its quiet ones.
A larger tank also holds more sludge before the level reaches the outlet, which lengthens the time between desludging visits. The Tricel Vento comes in three sizes, the UK6, UK12 and UK20, and each option on the product page lists its own capacity, so choosing comes down to matching that capacity to the people the property serves.
Installing a septic tank
The ground and the route the effluent takes decide how a septic tank goes in, so three checks belong before the order is placed.
Percolation test and drainage field
A percolation test, sometimes called a porosity test, measures how quickly water soaks away from trial holes dug where the drainage field will go. The result sets the length of drainage pipe the field needs, or shows that the ground will not take one, in which case a treatment plant or holding tank is the route. The plot also needs space for the field at a sensible distance from buildings, wells and watercourses.
High water table and rock
Trial holes dug in the wettest part of the year show where the water table sits and whether rock lies close to the surface. Water that enters the excavation is pumped out before the base goes in, using site pumps such as those in our washouts and pumps range, and on wet ground the tank is normally set in concrete so that it cannot lift when emptied.
Bedding, backfill and access for emptying
The tank sits level on a prepared base, and the backfill is brought up evenly around it so the body is supported on all sides. The position has to suit desludging too: a tanker needs a hard route to within reach of its hose.
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Frequently Asked Questions
How often does a septic tank need emptying?
A septic tank is desludged when the settled sludge builds up far enough to risk passing through the outlet into the drainage field. A desludging contractor can measure the sludge depth at each visit and set the next date from that reading.
Do you need a permit for a septic tank?
Most small domestic septic tanks that discharge to a drainage field can run without a permit, provided they meet the general binding rules for small sewage discharges. Larger discharges, or those in protected areas, need a permit from the environmental regulator, and a new installation also needs building regulations approval.
What should not go into a septic tank?
Wet wipes, sanitary products, nappies, cooking fat and food waste block the outlet and clog the drainage field. Bleach in quantity, solvents, paint and garden chemicals kill the bacteria that break down the sludge.
Does a septic tank need electricity?
No. A septic tank works by gravity and natural settlement, with no pump, motor or control panel, so it needs no power supply. A sewage treatment plant needs a permanent electricity supply to run its aeration. The only exception is a site where the drainage field sits higher than the tank outlet, which needs a pump to lift the effluent.
Can an old brick or concrete septic tank be replaced with a plastic one?
Yes. The old tank is emptied by tanker, then broken out or filled in place, and the new tank is bedded in the excavation and connected to the existing inlet pipe. The drainage field is checked at the same time, and if the old system discharged to a ditch or the soakaway has failed, the replacement includes a new drainage field or a treatment plant.