Gear Guides · A RidgeSong field guide
28 mm or 42 mm? Match DualFlow to Your Water Container
The opening matters more than the container name. A guide to DualFlow’s two inlet sizes, the new soft flask and the separate backwash connection.
Before you begin
- A flexible bag can have a narrow outlet.
- A slim soft flask can have a wide opening.
- The flask itself does not filter water, and DualFlow is sold separately from the single and duo flask packs.
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A bottle, a soft flask and a water bag can all play a part in a trail water setup. Their names do not tell you which connection they need. The opening and thread are what matter when you attach a filter.
DualFlow provides 28 mm and 42 mm inlet connections for compatible containers. Here is how to choose between them, including where RidgeSong’s new 500 ml soft flask fits.
Separate the container from the connection
A flexible bag can have a narrow outlet. A slim soft flask can have a wide opening. Choosing between 28 mm and 42 mm is therefore not the same as choosing between a bottle and a bag.
Start with the specification of the exact container. Then check whether its thread and seal fit DualFlow. A matching nominal diameter is useful information, but it is not a guarantee that every container labelled with that size will form a suitable connection.
The DualFlow design notes identify compatible beverage bottles and the optional RidgeSong 2 L bag as examples for the 28 mm inlet. The 42 mm connection serves compatible wide-mouth containers.
Three setups to compare
| Container | Relevant inlet | Why you might choose it | Check before packing |
|---|---|---|---|
| Compatible 28 mm beverage bottle | 28 mm | Use a suitable bottle already in your kit | Exact thread, condition and seal |
| Optional RidgeSong 2 L water bag | 28 mm | A larger source container for a planned refill routine | Connection and the complete filtering setup |
| RidgeSong 500 ml Collapsible Soft Flask | 42 mm | A flexible container that folds when empty | Verify the intended connection, fit and seal |
The 2 L bag and 500 ml flask have different capacities and different openings. Neither capacity tells you how much water your route requires. Choose your carried volume separately from your connection choice.
Where the new 500 ml soft flask fits
The RidgeSong 500 ml Collapsible Soft Flask has a 42 mm neck, a bite-to-drink mouthpiece and a flexible TPU body. It is listed as compatible with DualFlow for a separate filtering arrangement.
For ordinary drinking-water carry, the supplied cap and mouthpiece complete the flask. Attaching the filter is a different configuration; check the connection before heading out. The flask itself does not filter water, and DualFlow is sold separately from the single and duo flask packs.
If a flask has been used to collect untreated water, do not simply put the drinking mouthpiece back on and treat the contents as ready to drink. Plan the source and receiving sides of your setup before the trip, and follow the relevant cleaning and water-treatment instructions.
Check the seal at home
Try the actual filter and container together before relying on them in the field. Begin with clean components and drinking water. Align the connection carefully, check that it seats correctly and inspect for leaks while using the intended filtering mode. Stop if the thread does not engage properly; forcing a mismatched connection is not a fit test.
Also consider the container's shape when full. Can you hold it comfortably for squeezing? If you plan gravity filtration, is the container designed for the hanging arrangement you intend to use? A sealed inlet is one part of a usable setup.
This brief rehearsal can reveal a poor fit before it becomes a problem at a refill stop.
The backwash port is a separate connection
DualFlow also has a built-in 28 mm backwash connection on the outlet side, exposed by removing the drinking-outlet assembly. It is used with a compatible bottle of clean water to flush the membrane in reverse.
That port serves a maintenance job. It is separate from choosing the 28 mm or 42 mm inlet for source water. A 42 mm source container does not remove the need to plan a suitable clean-water bottle for backwashing.
Choose the fit, then the routine
Use the inlet that matches a verified compatible container, then decide whether you want a squeeze refill or a gravity setup. Keep the filter’s limits in mind: DualFlow is intended for suitable freshwater filtration and is not designed to remove viruses, salt or all dissolved chemical contaminants.
See DualFlow and its connection options, or compare the single and duo soft-flask packs if a compact drinking-water container is the next piece your kit needs.
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