Soft funnel for backpacking
A DIY soft funnel for spill-free and safe filling of a backpacking soft bottle hot water bottle or shower.
Background to the soft funnel
Backpacking soft bottle. A fellow tinkerer Steve Theultralighthiker has a post on using such a bottle as a shower where the water is heated separately in a pot (a 50:50 mix of cold and boiling water).
I have previously posted about the other backpacking uses for a backpacking soft bottle. They make a great high-capacity alpine hot water bottle and a bonus is that it ensures that you have unfrozen water for breakfast. I now use the bottle for both purposes and of course, to carry water.
Both the hot uses of the soft bottle require the pouring of hot water (often boiling) into a very small opening in the soft bottle. The pouring is made even more difficult when using wide backpacking pots that will invariably need to be quite full to do the job efficiently. If they are the most efficient backpacking pots, they will not have the amenity of a pouring spout and for my ultralight pots that are not pots, they will have no handle.
I figured that a lightweight soft funnel would nicely complement these hot uses of the soft bottle and it will even help when filling the bottle from the river at night while balancing on rocks in torch light.
A plastic screw cap from a soft drink bottle would make an obvious starting point (as we do to make a shower rose for the bush shower), but I did not have an effective way of glueing permanently to this plastic, so I settled on making the thread from rubber for my first try.
I later discuss simpler options that avoid the plastic glueing issue but I think the all silicone one will be the premium soft backpacking option and it will be fun to find out if it works. If it works, the method should be able to be used with other larger soft bottles (5L) that do not have compatible substitute lids such as those from regular soft drink bottles.
Consequently, the combination of RTV silicone rubber and shirt cotton fabric was my obvious choice of materials from my long list of backpacking uses for RTV silicone rubber.
Making the soft funnel from cotton and silicone rubber
Making a rubber thread. I started by wrapping the threaded part of the bottle with a temporary layer of cling wrap. Then I wrapped the cling wrap with cotton/polyester sewing thread several times to ensure that the cling wrap was pulled down into the grooves of the thread (This could be done better as described later). Next, I coated the screw thread and cotton thread with acetic cure RTV silicone rubber to form a female thread.
Using one of my favourite stretch fabrics that bonds well with silicone rubber, I cut strips or ribbons of pantyhose and wrapped the coated silicone rubber with this before coating it with more silicone rubber.
To speed the curing of the rubber, this female thread unit was sprayed with a mist of water. Lastly, it was wrapped in a temporary layer of cling wrap and the surface below was rendered even and smooth by massaging with my fingers through the cling wrap.
Making the cone. While the thread unit was curing I formed a cone shape out of shirt cotton. “Another wonderful silicone rubber compatible fabric favourite of mine.” This fabric had previously been impregnated with diluted TRV silicone rubber. This impregnation turns the bog ordinary cotton cloth into a fibre-reinforced rubber polymer. It makes it easy to mark out, cut and subsequently glue with silicone rubber. The impregnation also means that the fabric becomes very strong, waterproof and rotproof and will not fray or need sewn hems around the edges.
“I often use left-over impregnation mix for this purpose. It makes an excellent ‘thirsty’ cleaning cloth and then can be used for the next project without any waste. Multiple additions can be made to get the desired density.”
I cut the small end off the cone to leave a hole that was about half the diameter of the OD of the silicone female thread unit. Then I made radial cuts around the hole to form many little joining tabs. The depth of these cuts was made so that the thread unit could be squeezed in through the hole.
Then one by one, I lifted each tab and applied a dob of glue and then pressed the tab down onto the thread unit. More silicone rubber was applied over all the tabs and a final whipping of polyester/cotton sewing thread was applied. After another spray mist of water, a temporary layer of clingwrap was used to form a smooth finish.
Finishing touches. I glued on a silicone cotton handle on the outside of the cone to provide protection from boiling water splashes and a tethering point for an anchor cord (to prevent its loss). On the other side of the cone, I rolled the edge over and stuck it down with a generous layer of silicone to make this edge stiffer.
Finally, I clamped this stiffened edge between two layers of plastic (cut from an ice cream bowl lid), so that the cone would cure with an elongated shape. This helps to avoid spills when pouring from a wide-mouthed pot. “I think this embellishment was worthwhile and it certainly makes it look like the funnel that was formed on grandma’s old rubber hot water bottle. But this silicone rubber one won’t perish.”
A not quite soft funnel using an aluminium soft drink lid
It is time for an ode before we move on to the next iteration of the soft funnel:
Boiling water on camping fingers is bad stuff, Big pot, small hole makes decanting pretty tough, Make a wide soft funnel for the purpose fit, So snugly on soft bottle, it can securely sit, Just like Grans hot water bottle, funnely enough.
I could not glue a flexible cone to a plastic soft drink bottle lid. However, as I glued the cloth funnel to the DIY silicone thread I remembered that I could easily glue it to aluminium (As described in backpacking uses for RTV silicone rubber). There were plenty of those pressed aluminium lids that are often on glass drink bottles (apple cyder, coke etc.). A funnel made this way would be much simpler. It may get crushed a little during backpacking, but it would be easy to provide a protective dummy made out of the thread unit that could be cut off a plastic bottle.
To prepare the lid for glueing, I cleaned off some of the paint using sandpaper and a wire brush while leaving the lid on a glass bottle. Then I cut most of the top of the lid away using a stabbing action of a craft knife and then ground the edge to be smooth. I left a small ledge that would hold the polymer lid seal. Similarly, I cut a hole in the plastic lid seal and glued it into the lid with silicone rubber. I made a cotton silicone rubber cone as described above and glued it on in the same way, and used a wrap of impregnated pantyhose to bind and cover the attachment tabs.
Discussion & conclusion
If making another similar all silicone rubber device, I would not make the mistake of leaving the sewing cotton over the first layer of clingwrap or over the whipping on top of the attachment tabs. It formed tensile bands that stopped the thread from stretching while fitting it onto the bottle. I could not easily remove the sewing threads because they were strongly embedded in the rubber. A binding material such as a stretchy thin strip of pantyhose would be much better.
I think this funnel is a convenient addition for more safely and efficiently filling a soft bottle with boiling water and will also be good for cold water filling from a stream. I think the tether to attach the funnel (and the dummy) to the soft bottle will be essential to prevent its loss.
The simpler funnel that is made with an aluminium lid and silicone rubber/cotton was very much easier to make and is very convenient to use. Its hardness may need a little extra care in the choice packing position in the backpack. However, the plastic dummy should protect it from damage and can become a simple means of attachment to prevent loss. “So it is now my favourite funny funnel.”
Lastly, even if soft hot water bottles or hot bush showers are not quite your thing, this use of RTV silicone rubber should stimulate ideas for more backpacking DIY tinkering.
Tim
