The Norwesco 20,000 Gallon HDPE Underground Liquid Storage Tank (SKU N-41616) is a white polyethylene below-grade vessel built for high-volume underground liquid storage and septic service. At 20,000 gallons it measures 665 inches long, 101 inches wide, and 107 inches tall - roughly 55.4 ft x 8.4 ft of footprint standing 8.9 ft tall - which makes it one of the largest single-piece underground polyethylene tanks Norwesco molds. It ships from Norwesco's St. Bonifacius, Minnesota plant.
Will this tank work for your site?
This is an underground HDPE tank sized for large-scale water, wastewater, and septic applications. The footprint is 101.0 x 665.0 inches (about 8.4 ft x 55.4 ft), so before you order, confirm your excavation length, bedding, and burial depth can accommodate a vessel this long. Filled with water, the tank carries a full water weight near 166,800 pounds against the surrounding soil - that is the load your backfill and site engineering have to support. Because this is a buried tank, proper bedding, uniform backfill, and adherence to Norwesco's burial guidelines matter more here than on any above-ground vessel. If you are still confirming that 20,000 gallons matches your demand, run the numbers with our Tank Sizing Calculator and review the Tank Sizing Guide. Fittings and outlets are not published as a structured spec for this tank - see the technical drawing on this page for fitting locations and dimensional detail, and size your manifold, bulkhead, and gasket connections from it before finalizing your plumbing layout.
Key specifications
The points that drive a buying decision on a tank this size:
- Capacity: 20,000 gallons
- Dimensions: 665 in L x 101 in W x 107 in H (55.4 ft x 8.4 ft x 8.9 ft)
- Full water weight: approximately 166,800 lb
- Material / color: HDPE polyethylene, white
- Service class: underground water/wastewater and septic
- Specific gravity rating: not published - water and wastewater service only
- Fittings/outlets: per technical drawing (not published as a structured spec)
- Ships from: St. Bonifacius, MN (single plant)
The mistake to avoid
The specific-gravity rating on this tank is listed as "No," meaning it is not published with a liquid specific-gravity figure for fluids denser than water. Treat it as a water-and-wastewater tank: water storage, rainwater, fire-water reserve, and septic service. Do not assume it is rated for heavier-than-water liquids without written confirmation - if your application involves a denser fluid, call us at 866-418-1777 before you spec it rather than guessing. This is also a septic-classified tank, so if your install is a septic system, verify the unit carries the approvals your jurisdiction requires before you set it in the ground. Norwesco's septic approvals vary by region and code; our guide on Norwesco IAPMO and CSA B66 septic tank approvals walks through the cross-border scope versus US plumbing codes. For a rural fire-water reserve, our fire-water reservoir design guide covers NFPA 22 sizing discipline and cold-climate freeze protection.
Wall thickness and long-term durability
For underground HDPE storage and septic tanks like this one, wall integrity and design life are worth understanding before purchase. Our breakdown of HDPE tank wall thickness at the vapor-saturated headspace explains where premature failures originate and the ASTM D1998 sizing logic operators should know. If any portion of the install lands above grade or on a pad, the concrete pad sizing guide covers the ACI 360R-10 framework.
This tank ships LTL freight from a single origin - Norwesco's St. Bonifacius, Minnesota plant - quoted live to your ZIP code, so haul distance is the main driver of your delivery cost (a buyer in CA or TX will see a longer LTL run than one in the upper Midwest). Given a vessel that runs roughly 55 feet long and weighs about 166,800 pounds when full, get an accurate delivery number before you commit using our Freight Cost Estimator, or call us at 866-418-1777 to plan delivery and offloading for an underground tank of this scale.
