Robert Bills
Explorer
How-To: Rotopax Water Can Siphon
Running Water for Only $10
Running Water for Only $10
Rotopax 2-gallon water cans are a convenient way to carry water for car camping or overlanding. They can be stored vertically or horizontally, inside or outside you vehicle, and the compact size makes it possible to fit them into spaces where larger jerry cans and those ubiquitous blue water jugs cannot. However, there is one niggling inconvenience when carrying a Rotopax water can inside your vehicle, especially when it is surrounded by other gear – before you can get to the water you generally have to unpack some gear, remove the can and install the spout, pour the water, and then put it all back when you are finished. What a hassle.
There is a better way – a siphon tube.
Your siphon can be as simple as a length of aquarium airline that you suck on to prime, or a more elaborate system with a squeeze bulb primer and valve to control the flow. You can even go “expo style” with food grade tubing, brass or stainless steel fittings and a battery powered pump to fill your $50 titanium water bottles as fast as you can at home.
What I did, using parts readily available at my local home brew store and stuff in my garage left over from other projects, is make a siphon tube with a beer tap faucet to start/stop flow and utilize a separate air tube that one blows into to pressurize the can and prime the siphon. Simple and cheap with no moving parts.
Now I can have running water for cooking and washing up in seconds without pulling my Rotopax can out of my truck or having to move any other gear out of the way. I carry one Rotopax can inside and up to two more on my roof rack. When the inside can is empty I simply exchange it for one from the roof.
Sixth grade science class finally paid off!
Parts/Supplies needed:
1/4” O.D. copper or rigid plastic tube (6” or so) – Free (leftover from another project)
1/4" I.D. clear vinyl tubing (6” or so) – Free (leftover from another project)
3/8” O.D. copper tube or rigid plastic tube (6” or so) – Free (leftover from another project)
3/8” I.D. clear vinyl tubing (I used 7’ @ $0.69/ft.) - $4.83
Extra Large Nylon Tubing Clamp to fit 3/8” I.D. vinyl tube (optional) - $1.50
1 pre-drilled #7 rubber stopper - $1.29
Faucet – Picnic Tap - $3.99
2 #000 small rubber stoppers (optional), $0.45 ea. - $0.90
Velcro strip to secure tubing when not in use (optional) – Free (leftover from another project)
Total Cost: $12.51 plus tax. Cost without optional items, $10.11.
Tools needed:
Dremel with cutoff wheel or hacksaw to cut copper tube
Scissors to cut vinyl tube to length
Small piece of sandpaper or emerycloth to dress cut edges
Drill
3/16” drill bit to drill a second hole in rubber stopper for copper tube
Knife or razor blade to trim velcro strip
Windex or glycerine or spit to aid in assembly . If you don’t have any of those and aren’t a spitter, you can use a tiny bit of vegetable oil.
Pencil or Sharpie
Time Required:
30 minutes once you have assembled all the supplies and necessary tools.
Degree of Difficulty:
Easy, peasy.
Putting It Together:
Put your Rotopax can where is will be stored when you are packed for an excursion, whether it be a Rotopax brand mount or strapped/bungied in place. For this siphon project to be of any use the Rotopax can will need to be someplace where you can access it simply by opening a door or rear hatch. Remove the Rotopax cap and put the yellow spout and sealing disc someplace where you can find them later.
Place the #7 stopper with the predrilled hole in the fill hole of the Rotopax container. Tighten the plastic Rotopax threaded cap (with hole in center), ensuring that the stopper is inserted straight and the rim on the threaded cap engages the stopper all the way around.
With the stopper in place and the Rotopax cap tightened, lubricate the 3/8” copper or rigid plastic tube and push it through the hole until about 2” is showing inside the can (you can adjust this later). Then, using a 3/16” drill bit, drill a hole in the rubber stopper centered midway between the edge of the 3/8” tube you just pushed through the stopper and the inside edge of the rim of the Rotopax threaded cap. Be sure that your drill bit is straight – you want the two tubes to be parallel, leaving enough rubber between the holes so that you have a good seal. [Hint: It works better to drill with the stopper inserted in the Rotopax can. I tried other methods and ruined two stoppers.)
Push the smaller piece of copper or rigid plastic tube through the hole you drilled until about 1-2” is showing inside the can (as with the larger tube, you can adjust this later.)
Remove the stopper from the Rotopax can. Take your long piece of 3/8” vinyl tubing and place it into your Rotopax can until the tube is at the bottom of the can. Mark the length at the fill hole and cut. Push one end over the rigid tube that you ran through the pre-drilled hole in the center of your #7 stopper until it touches the stopper, ensuring that about 2” of the rigid tube is showing. If necessary, trim the rigid tube on the outside of the stopper so that about 2” is showing there as well.
Adjust the smaller diameter rigid tubing that you ran through the hole you drilled so that 1-2” is showing on the inside of the stopper and about 2” on the outside. Trim the length if necessary. Put the stopper back on the Rotopax can and measure from the stopper to a comfortable place for you to blow into the tube without hitting your head on something, then cut a piece of 3/8” tube to that length. (Note: Keep this length of tube as short as practicable. Also, what I had to do to get a tight fit between the 1/4” OD copper tube I used for the smaller hole and the 3/8” ID tube was place a 1 1/2" long piece of scrap 1/4” ID vinyl over the copper tube and then push the 3/8” tube over that. This resulted in a tight seal without having to resort to a hose clamp.)
Now, with the #7 stopper still inserted in the Rotopax can, measure the length of 3/8” tube you need for filling pots, etc. Be sure that this location is below the bottom of the mounted Rotopax can or your siphon will not work. Cut the tube to that length and push onto the rigid tube in the center of the #7 stopper.
Insert the picnic tap faucet into the end of the long tube. As with the air pressurizing/priming tube, I needed to use a short piece of scrap tube as a sleeve to get a tight fit. Again, this resulted in a good seal without having to use a hose clamp.
You are done. Time to test your siphon.
Operating Your Siphon:
Fill your Rotopax can to the fill line. Run the pickup tube to the bottom of the can, push the stopper into the fill hole, then tighten the threaded Rotopax cap.
Holding the picnic tap faucet open with your thumb, with the faucet below the bottom of the Rotopax can, blow into the short tube until water begins to flow through the faucet. That’s it! Your siphon is now primed and you will have running water on demand as long as you keep the faucet below the water level and the priming tube open to atmosphere (a closed priming tube creates a vacuum as the water level drops, with resulting decrease in water flow).
What is the purpose of the velcro strip and optional nylon tube clamp and small stoppers?
I cut a slit in two velcro stips to cinch around the long vinyl tube in two places as ties to keep things neat and orderly when the siphon is not in use.
I put the tube clamp on the pressurizing/priming tube so I can close the tube when the siphon is not in use to keep dirt and bugs out.
What about the small stoppers? You will lose them. I’ve already lost mine. The tube clamp is a better idea.
Enjoy!
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P.S. – These websites were my inspiration for this project:
What did you do to your Expo Jeep today? - Page 344 - Expedition Portal
Running Water for the Jeep - Vagabond Expedition
3 Ways to Make a Siphon - wikiHow
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How To Siphon Beer Into Bottles : No Sucking, No Auto-siphon, No Mess
https://youtu.be/2-F_RBWVxmk
Note: I tried the linked Carboy siphon cap method on my Rotopax cans, fitted over the Rotopax threaded cap. It didn’t work - too much air leakage around the cap made the siphon impossible to prime.
