Coliwasa Samplers: Types, Use, and Selection Guide for Canada

A coliwasa — short for COmposite LIquid WAste SAmpler — is the standard tool for pulling a representative sample from a drum or tank of layered, viscous, or unknown liquid waste. It captures a full vertical column in one stroke, so the lab sees every phase in proportion: the floating organics, the water layer, and the settled sludge. This guide explains how a coliwasa works, how to use one correctly, and how to choose between glass, PTFE, and polyethylene for your waste stream.

What Is a Coliwasa Sampler?

A coliwasa is a long tube fitted with an internal valve or stopper at the bottom end, used to collect a representative column of liquid from a drum, pail, tank, or tanker. The name is an acronym: COmposite LIquid WAste SAmpler. Its defining feature is that it captures a vertical cross-section of the container's contents — not just the surface — which is the only way to fairly represent a liquid that has stratified into layers during storage.

That matters because liquid wastes separate by density. Solvents and oils float, water sits below, and solids settle to the bottom. A sample taken only from the top would miss the heavier phases entirely and misrepresent the waste — and the waste classification, transport code, and disposal route all hinge on that result. The coliwasa exists to solve exactly this problem, which is why it is the default device for characterizing drummed hazardous and industrial liquid waste. It belongs to the broader family of drum and tank liquid sampling equipment, where it occupies the multiphase-and-unknown-waste niche.

How Do You Use a Coliwasa Sampler?

You use a coliwasa in three steps: lower it open to fill, close the valve to seal the column, then withdraw and transfer. Done correctly, the result is a representative composite sample of everything in the container. The detail in each step is what makes the sample valid.

1. Lower it in fully open. With the bottom valve or stopper open, lower the coliwasa slowly into the drum or tank. Liquid enters the tube and rises to the same level as the surrounding waste, so the column inside the tube mirrors the layers outside it. Lowering slowly prevents the inner level from lagging the outer level, which would bias the sample.
2. Close the valve at the bottom. Once the sampler reaches the bottom and the tube has equalized, close the internal valve (by pulling the inner rod or rotating the locking mechanism, depending on the model). This seals the full column inside the tube so nothing drains or re-mixes on the way out.
3. Withdraw and transfer. Lift the sealed coliwasa out, wipe the exterior if required, position it over the sample container, and open the valve to release the column into the bottle. The transferred sample now contains every phase in proportion.

Two field notes: work with appropriate PPE because the operator is over an open container of potentially hazardous liquid, and use a fresh or decontaminated sampler for each waste stream to avoid cross-contamination. For unknown or hazardous drums, a disposable coliwasa removes the decontamination question entirely.

When Should You Use a Coliwasa Instead of Another Sampler?

Use a coliwasa when the liquid is stratified, viscous, multiphase, or unknown — and a simpler sampler when it isn't. The coliwasa's strength is full-column capture, which is wasted effort on a clean, uniform liquid.

• Use a coliwasa for: drums of mixed waste, oil-water layers, sludges and semi-solids, viscous liquids, and any container whose contents are unknown and must be characterized.
• Use a drum thief instead for: clean, free-flowing, single-phase liquids where any full-depth column is already representative — a drum thief is faster and lower-cost.
• Use a sub-surface or weighted sampler instead for: a sample from one specific depth rather than a full composite — for example, the bottom layer of a large tank. ERE's sub-surface samplers serve this case.
• Use a dipper instead for: surface or near-surface grab samples from open-top containers where a composite isn't required.

What Are Coliwasa Samplers Made From?

Coliwasa samplers come in glass, PTFE, and plastic, and the right material is the one chemically compatible with your waste. Picking the wrong material risks a sampler that the liquid attacks, contaminates, or weakens during use.

Glass Coliwasa Samplers

Glass (borosilicate) offers broad chemical resistance across solvents, acids, and oils, and it lets the operator see the captured column and its phase boundaries through the tube. ERE's glass coliwasa samplers (Conbar) come in Viton, PTFE, and ground-joint seal configurations in 18" and 42" lengths. The trade-off is breakability, so glass is chosen where chemical compatibility and visual inspection matter more than ruggedness — and disposable pre-scored glass versions are common for single-use hazardous sampling.

PTFE Coliwasa Samplers

PTFE (Teflon) is the most chemically inert option, standing up to aggressive solvents and strong acids that would attack glass seals or plastics. ERE's PTFE coliwasa samplers are the choice for the harshest or most tightly regulated waste streams where nothing less inert is acceptable.

Polyethylene and Plastic Coliwasa Samplers

Polyethylene and polypropylene coliwasa samplers are economical and unbreakable, well-suited to aqueous wastes, dilute acids and bases, and disposable single-use sampling. ERE's polyethylene coliwasa sampler is the practical default for routine aqueous waste and high-volume disposable use. Plastic is not suited to aggressive organic solvents, which can soften or permeate it.

How Do You Choose the Right Coliwasa?

Choose by working through four inputs: waste chemistry, container depth, disposable versus reusable, and seal type. Each one narrows the options.

• Waste chemistry sets the material — glass or PTFE for solvents and acids, polyethylene for aqueous and mild wastes.
• Container depth sets the length — a standard 42" coliwasa reaches a typical drum; deeper tanks and tankers need longer tubes or a sub-surface sampler.
• Disposable or reusable follows from contamination risk — disposable polyethylene or pre-scored glass for unknown and hazardous waste, reusable glass or PTFE for repeated sampling of a known, compatible liquid.
• Seal type (Viton, PTFE, or ground-joint, in ERE's glass line) sets the chemical compatibility of the closure itself and how leak-free the seal needs to be for the waste being sampled.

If you're not sure which configuration fits your waste profile, the liquid and water sampling collection shows the full range, and ERE's technical team can match a coliwasa to your stream from the waste description.

What ERE Supplies for Coliwasa Sampling

ERE Inc. has supplied environmental sampling equipment across Canada for 30+ years, with coliwasa samplers stocked and shipped from Montreal with bilingual technical support. ERE carries the Conbar coliwasa line in glass (Viton, PTFE, and ground-joint seals, 18" and 42"), PTFE for aggressive chemistries, and polyethylene for economical aqueous and disposable sampling. Replacement seals and valves are available to keep reusable units in service.

The coliwasa is one tool in ERE's complete drum and tank sampling range, alongside drum thiefs, dippers, and sub-surface samplers — see the drum and tank liquid sampling guide for how they compare. Send your waste type, container depth, and seal preference and our team will recommend a compatible coliwasa.

Frequently Asked Questions

What does coliwasa stand for?

Coliwasa stands for COmposite LIquid WAste SAmpler. The name describes its job: collecting a composite sample of a liquid waste by capturing a full vertical column rather than a single-depth grab.

How do you use a coliwasa sampler?

Lower the coliwasa into the drum or tank with the bottom valve open so liquid fills the tube to the surrounding level, close the valve to seal the captured column, then withdraw the sampler and open the valve over your sample container to release it. The result is a representative composite of every layer in the container.

What is the difference between a coliwasa and a drum thief?

A coliwasa has an internal valve that seals the captured column, so it holds a representative sample of layered or multiphase waste. A drum thief is a simpler open tube capped by thumb or stopper, best for clean single-phase liquids. Use a coliwasa for stratified, viscous, or unknown waste and a drum thief for homogeneous liquids.

Should a coliwasa be glass, PTFE, or plastic?

Match the material to the waste: glass for broad resistance and visual inspection, PTFE for the most aggressive solvents and acids, and polyethylene for economical aqueous or disposable sampling. Plastic is not suitable for strong organic solvents, which can soften or permeate it.

Related articles

• Drum and Tank Liquid Sampling: Equipment and Methods Guide
• Environmental Sampling Equipment Guide for Canada
• Groundwater Bailers: Types, Materials, and Selection

Lire en français : Échantillonneurs coliwasa : types, utilisation et guide de sélection pour le Canada