Slurry Transfer in Solventless Processing : Gravity Drain or AODD? - SC Filtration

Slurry Transfer in Solventless Processing : Gravity Drain or AODD?

Hash making is comprised of two main portions, Agitation, and Filtration. However, an often under-looked component is the bridge between these two steps, slurry transfer! 

After agitation, the slurry in solventless extraction needs to be filtered. To do this, regardless of the method used to agitate, we must transport it from point A (Agitation) to point B (Filtration). In general, there are two methods of moving the trichome-laden slurry:

  1. Gravity Drain
  2. Pump Assisted 

Each of these methods has benefits, however, not all methodologies are created equal. So, it comes down to the question. Which is ideal? Using a simple comparison of the Pros and Cons of each method we will delve into which is the correct route to go for the average hash lab.

Gravity Draining

Gravity draining starts with a very simple precondition, the lowest upfront cost. Simply setting up a high enough platform with a catch basin underneath for bags is all that is needed. Brew kettles, 20/32-gallon brutes, and 20-gallon washers tend to use this method of draining.


An argument can always be made for simplicity, The benefits of gravity draining on its face can be enticing to the craft producer or hobbyist.

  • Lowest starting cost of entry, aside from furniture. Having to deal with only the cost of handwashing set up in the lower volume range can be beneficial to smaller operations
  • Very short drain times which if used correctly can shorten wash times.
  • Fewer items to sanitize and overall less maintenance. Having a shorter reset time between washes and workdays can be crucial to some operations.
  • 100% trichome safe prefiltration. You can rest assured that a 90-degree angled spout won’t harm your heads.
  • No air compression or electricity is required, making this method reliable for smaller & mobile operations as well as much quieter.
  • Gravity draining is essentially a zero-maintenance option


Free isn’t cheap! The low upfront cost of gravity setup will quickly add up to more in time, effort, and ancillary needs. By limiting ourselves to the near terminal velocity of falling water, we introduce several other risks and limiting factors such as:

  • Agitation machine options in terms of scalability are incredibly limited, essentially just 20-gallon plastic washers or some form of handwashing. Neither of which have a place in a consistent commercial setting.
  • The pressure of the flow can be controlled only 2 ways, by aperture size, which should generally stay at 1.5 inches, and by the volume of the container. The more water in the container, the higher the PSI at the spout! Overall lacking in control.
  • Requires manual valve opening and closing adds to workflow needs.
  • High-pressure flow with heavily trichome-laden water will cause excess smearing on bags, especially with vessels over 50 gallons. The velocity of the slurry against the porous surface acts like a cheese grater!
  • Processes require overhead lifting, stairs, and general labor overall.
  • Cannot be used in conjunction with controlled flow processes such as vibrational sifters or other dewatering technologies
  • If using a mechanical agitator, gravity drainable options also tend to have a bottom-driven motor. Due to the height needed to drain into the correct volume containers, the motor is often placed directly underneath the agitator. Constantly adding heat energy to the wash.
  • Should errors like bags slipping, or a drain valve not being closed on a collection vessel occur, the flow rate of the gravity drain is likely to cause much larger incidents of spillage or cross-contamination between bags from excess motion in the water.

AODD Pump Draining

An Air-operated Double Diaphragm pump enters the lab with a whole slew of benefits; while some of these benefits incur equipment costs, they tend to be in the form of long-lasting and maintenance-free objects like tri-clamp fittings and valves.

Trichome Pump


  • Control over the velocity of the slurry.
  • Self-priming! AODD pumps create their own vacuum and can run dry.
  • Removes the need for raised agitators, reducing the footprint of a washing setup.
  • Increases workplace safety, reducing spills.
  • Generally, trichome safe with the right pump.
  • An AODD can be plumbed in such a way that the highest point of the pipe is taller than the max fill line of the agitation, Removing the need for valves in several scenarios.
  • With a simple manifold setup, a single AODD can be used in all instances of moving water in a hash lab.
  • Easily synced with other AODDs using air pressure regulators.
  • Multiple-AODDs can be run on a single air line, removing the need for electrical cords in the often-wet environment.
  • The pulsation of the alternating diaphragm helps keep trichomes afloat in a stream. The consistency of gravity draining, and centrifugal pumps tends to allow for inconvenient settling.
  • General maintenance required is easy.
  • Low cost in comparison to lifespan.
  • Available as an FDA approved device from certain manufacturers (Including SC Filtration)
  • Sanitary Tri-clamp compatible (some may require NPT parts to do so) allowing an AODD to be used with nearly any model of existing agitator.
  • Easily mounted to an equipment rack or existing dolly.
  • A necessary component of any closed-loop or vibrationally assisted system!


While limited, the cons of an AODD revolve mostly around make and model and can be impactful. Like any other equipment, your source’s quality is paramount! With every single trichome processed going through one of these, it can be well worth the research required to find a suitable model.

  • Not all pumps are considered trichome safe, though they will be mostly trichome safe, “check ball” style pumps can get minor blockages, causing shearing. Only trust specific, well-researched suppliers.
  • Not all AODD pumps are sanitary. Models must be of food-grade plastic or stainless steel to pass rigid operating standards.
  • Trustworthy models can cost up to $2000+.
  • An AODD does require upkeep and maintenance, which must be factored into operations procedures at least weekly.

From this perspective, choosing to operate with AODD pumps in place of gravity draining is the most effective choice for a laboratory looking to expand while reducing workload. While a lower budget operation may find benefit in the savings of a gravity drain set up at first, it will quickly add up in labor, time lost, and accidents.

Overall, my recommendation for hash labs first upgrade is going to be an AODD pump. Do your lab a favor and find yourself a strong, quiet air compressor and a reliable manufacturer of these devices to begin reaping the various benefits they can offer.

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