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Silt Bag for Drain Inlet: Drop Inlet Sacks Explained | Mainline Materials
Silt Bag for Drain Inlet: Drop Inlet Sacks Explained
What a drain inlet silt bag is, how it installs, and how to size it
In This Guide
A silt bag for a drain inlet is a fabric bag that hangs below a storm grate to catch silt and sediment from runoff before it enters the drain. Often called a drop inlet sack or catch basin silt sack, it installs on the grate without rebar, collects sediment in the bag, and is emptied and reused. It is one of the simplest and most popular inlet protection devices.
Quick answer: A silt bag for a drain inlet is a fabric sack that hangs below a storm grate, catching silt and sediment from runoff while filtered water passes through.
What is a silt bag for a drain inlet?
A silt bag (drop inlet sack) is made from strong filtration fabric, often safety-orange monofilament geotextile, shaped into an open-top bag. It sits under the grate so runoff passes through the grate, into the bag, and out through the fabric, leaving silt and sediment captured inside. Internal straps cradle the grate for support during install and removal, and the open top lets water bypass safely in heavy rain.
How it installs and works
- No rebar needed: the bag installs directly on the storm grate, held by the grate itself and its internal straps.
- Filtration: sediment-laden water enters the bag and the fabric filters out silt and sediment.
- Overflow protection: the open-top design lets water bypass over the rim if the bag fills or clogs in heavy rain, so the inlet does not back up.
- Reusable: empty the captured sediment and reuse the bag across a project.
Sizes and variations
Silt bags for drain inlets come in four standard sizes to match common grate openings, with custom sizing available to fit nearly any opening. The standard model suits typical flat drop grates, while a framed model adds a metal frame for extra rigidity and strength on heavy-traffic or demanding inlets. All Dandy inlet products are made in the USA.
Choosing the right silt bag
Measure the grate opening and pick a bag sized to it, then decide whether a standard or framed model fits your traffic and duty needs. For non-grate or curb inlets, a different device such as the Dandy Curb Sack is the right tool instead. The Inlet Protection Product Selector can confirm the match.
Not sure which product fits your site? Use the Inlet Protection Product Selector, our free interactive tool under the Resources menu, to answer a few plain-language questions and get matched to the right inlet protection device, type, and size for your storm drain or curb inlet.
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Shop Inlet ProtectionUse the Inlet Protection SelectorFrequently Asked Questions
What is a silt bag for a drain inlet?
A silt bag for a drain inlet is a fabric sack that hangs below a storm grate to catch silt and sediment from runoff while filtered water passes through. It is also called a drop inlet sack or catch basin silt sack.
How does a silt bag install?
A silt bag installs directly on the storm grate without rebar, held in place by the grate itself and its internal straps. Runoff passes through the grate into the bag, the fabric filters out sediment, and the open-top design lets water bypass over the rim in heavy rain.
Are silt bags reusable?
Yes. Most drop inlet silt bags are reusable. Crews empty the captured sediment and reinstall the bag, which makes it a practical, low-cost option across the life of a project.
What sizes do silt bags for drain inlets come in?
Drop inlet silt sacks come in four standard sizes matched to common grate openings, with custom sizing available for nearly any opening. A framed model adds rigidity for heavy-traffic or demanding inlets.
When should I not use a silt bag?
A silt bag is made for flat drop grates. For curb-face or grateless inlets, a curb filter or barrier designed for the gutter line is the right device instead.