The Snyder Industries 405 Gallon ASTM Black Double Wall Tank is a contained-storage vessel for installations where a single skin is not enough and a secondary barrier has to catch a leak before it reaches the ground. The primary tank is molded from high density linear polyethylene rated to a 1.9 specific gravity, and the integrated outer wall provides interstitial containment in one nested unit. It holds 405 gallons, stands 73 inches tall on a 48 by 48 inch square footprint, and the black resin blocks light to slow algae growth on water and water-adjacent service. Because it ships LTL from Chowchilla, California, the smartest first move is to price your delivered freight: run your ZIP through the Freight Cost Estimator before you order.
Will this double wall tank work for your install?
Size your pad to the load, not the nameplate. Filled with water this tank carries about 3,378 pounds; at its full 1.9 SG rating it is engineered to support up to 6,418 pounds of contents. That roughly 3,040-pound spread is the number that catches people out, so build to the higher figure if you will ever store anything denser than water:
- Water service: 3,378 lb full
- Maximum rated load at 1.9 SG: 6,418 lb
- Footprint: 48.0 x 48.0 in • Height: 73 in
That 1.9 SG rating is the real differentiator here. Most water tanks stop at water; this double wall holds heavier liquids up to the 6,418-pound contents limit, so it does double duty when your service may change. Plumbing and venting route through a single documented penetration: the 18-inch PE threaded and vented top opening. There is no second outlet, so confirm your bulkhead, threaded fittings, and gaskets match that 18-inch PE threaded port before you order. Interior reach comes from one manway with 15-inch access, which is your only route to inspect both the primary tank and the interstitial gap. See the technical drawing on this page for fitting placement and the secondary-containment geometry before you set the tank. If you are still working out whether 405 gallons matches your draw and refill cycle, run it through our Tank Sizing Calculator and the Tank Sizing Guide.
Sizing the freeboard correctly
Usable volume is not the same as nameplate volume. At a 1.9 SG rating you have to reserve freeboard for thermal expansion, so the gallons you can actually fill sit below 405 once you account for density and temperature. Compute your real usable volume with the sizing calculator using the 405-gallon and 1.9 SG inputs, then read the deep dive on Snyder Captor double-wall freeboard sizing per ASTM D1998 to see how density and temperature change that figure. The companion piece on HDPE tank wall thickness at the vapor-saturated headspace covers where premature failures originate and why liquid-side inspection misses them.
The mistake to avoid
The most common error on a double wall tank is treating the interstitial space as set-and-forget. The outer wall exists to contain a primary-tank leak, so it has to stay accessible and dry. Use the 15-inch manway to inspect the primary tank and the interstitial gap on a schedule rather than only checking the liquid side. If this tank is part of a fire-water or emergency-reserve plan, the fire-water reservoir tank design guide covers NFPA 22 sizing discipline and freeze protection for cold-climate sites. For buried or steel-adjacent secondary-containment work, the reference on cathodic disbondment testing for double-wall interstitial spaces details the ASTM G8, G42, and G80 methodology.
This Snyder double wall tank ships LTL freight from the Snyder plant in Chowchilla, California, with the cost quoted live to your ZIP code. Get a delivered freight estimate before you order using our Freight Cost Estimator, or call 866-418-1777 and our team will price the freight and confirm the right black double wall tank for your site.
