Rigging a stage bottle – although not something taught in an SDI openwater class – is nevertheless a basic scuba skill. Certainly, it is one of the first things an instructor will discuss with aspiring tech-divers who almost always carry an extra scuba cylinder (or cylinders) with them on all their underwater outings. However, like so much about dive gear and dive practices, there are several tenable solutions, though none work perfectly for every application. In other words, the correct way to rig a stage bottle depends on exactly how you intend to use it!
To find out which options best suit a particular need, we should start at the beginning by asking, “What exactly DO we mean by a ‘stage bottle’ and what purpose is it intended to serve?”
Technically, a stage bottle is a cylinder containing gas that is going to be “staged,” or stashed, during a set-up or preparatory dive along a predetermined route – such as in a cave passage. At some later date, divers will travel along that route, and the stage bottles will help ensure they have something to breathe! Staged gas allows divers to travel further and swim longer than they would if their excursions were limited to only the gas that they could physically carry with them.  Staging gas is an explorer’s trick, and the gas contained in a stage bottle is sometimes left as a contingency and sometimes as part of the overall gas consumption plan.  Often stage bottles are left behind after the “big” dive and collected on a later clean-up dive.
Now, many divers will find this definition to be disagreeable, but take a deep breath because there are a lot more where that came from! A stage bottle is a general term used to describe a cylinder that is carried by a diver in addition to the primary scuba gear (open or closed circuit). A stage bottle can be a cylinder of decompression gas (for staged deco diving), a cylinder of travel gas to help a diver get from the surface to a depth at which his back gas is suitable to breathe (as in with hypoxic trimix), or an additional cylinder of bottom mix carried by the diver throughout his dive to add a level of security should something go awry with the primary gas supply.

Additionally, a stage bottle can be a cylinder of bottom mix used as the main gas supply with primary cylinders as backup ( a common practice with divers riding Diver Propulsion Vehicles), a bailout open-circuit gas for a CCR (closed-circuit rebreather) diver to have if they have to “come off the loop” (jargon to describe the situation when all bets are off and their CCR is not safe to use), a pony bottle carried by a sport diver to provide emergency gas for an Out Of Air event, or a buddy bottle to allow a self-sufficient diver (SDI Solo Diver for example) to have back-up gas and an abundant gas delivery system when diving independent of their buddy.

Wow! Who knew?
On top of that list of applications – or perhaps because of it – stage bottles come in all sorts of shapes and sizes (the shapes are universal, but sizes and cylinder materials vary). The most common stage bottles used by technical divers are the aluminum 80 cubic foot (11 litre) cylinders and its 40 cubic foot (6 litre) little brother. Some divers – particularly sport divers – use smaller cylinders than these as pony bottles. Similarly, a few divers use larger volume cylinders including steel tanks, but when technical divers speak about stages or deco cylinders, the majority have an aluminum 80 or 40 cubic foot in mind.
Quite simply, these are favorites because of low cost, durability, availability, the volume of gas they carry and their buoyancy characteristics; both the 80 and 40 have a very slight apparent weight in water and both tend to “sit” nicely close to a diver’s body, which is a function of their overall length, diameter and buoyancy.
Common to all forms of stage bottles, regardless of their final application, is that they need to be rigged in a way that allows them to be carried by the user without getting in his way and hampering his progress through the water. In other words, ALL stage bottle rigs have to be streamlined and create the least possibility of snagging line, getting hung up in kelp, digging a trench in the mud or smashing against rocks, boats, wrecks, coral etc. In addition, most divers want their stages rigged so that they have unlimited access to its valve and the regulator first stage that will be attached to it.
Speaking of regulators, a working stage bottle will feature a good quality first stage with an SPG (often on a short hose) and a single second stage on a hose long enough to route comfortably to the user’s mouth with the bottle in position. Depending on actual application, the first stage regulator – especially on CCR bailout bottles – may also have a low-pressure inflator hose attached. (See photo).
Finally, most experienced technical divers want their stages configured in a way that allows them to be donned and doffed quickly and without fuss.
With this in mind, by far the most functional rig for the majority of technical divers is one that attaches the stage to the diver’s side and close to his body using a couple of bolt snaps. This is vastly preferred to attaching stages to backmounted primary cylinders; although, one can still see old-school divers with the cylinder containing their decompression gas shoehorned between their doubles behind their back and well out of reach. This backmounted option is also popular among sport divers who sometimes attach a pony bottle to their single primary cylinder with proprietary hardware. On the plus side, it does keep things out of the way; on the negative side, it does keep things out of the way. In other words, out of reach and out of visual contact, when rigged like this, offers no way to manipulate the valve or do a visual check without taking everything off.
So, we find ourselves with an aluminum 80 (or a 40) and a regulator setup just the way we want it. (See photo). Now we need to put some bolt snaps on it.
Here we have a couple of options:
The traditional tech-diver method (actually known as the traditional North Florida Cave Diving method) is to tie two bolt snaps to a length of string, slip that string onto the neck of the stage bottle and attach the bottom end using a stainless steel pipe clamp.  This method is so ubiquitous that various scuba gear manufacturers sell “stage bottle kits” containing all the necessary hardware.  At the time of my last check, this past Saturday, my local dive shop carried pre-made stage bottle kits from three different main-stream technical diving brands. (See photo).
These kits make life simple and since none come with instructions, they must be easy to fit, correct? Well, not exactly. One small refinement often left out of the plan is to “optimize” the location of the lower anchor point so that it fits the diver. This helps to make clipping and unclipping the bottom bolt snap easier and will help to keep the bottle as close as possible to the diver’s body, especially the neck of the bottle.
The trick is to adjust the distance from the clip at the neck of the stage bottle and the lower anchor point so it’s the same as the distance between the Dring on the diver’s shoulder harness and the one on his hip. Since most of the ready-made kits available seem to be made to fit someone about 185 cm tall (about six feet), this exercise usually requires shortening the pre-made string “handle.” (By the way, NEVER carry a stage bottle by its handle; you should carry it strictly at its valve. The handle is for moving bottles around in the water. Carrying a stage incorrectly will stretch the cord and could break it).
A growing trend among both open-circuit and CCR divers is to rig their additional cylinders as sidemount stages.  Sidemount rigging requires an additional piece of equipment – a butt plate – and a strategically placed, moderately stout bungee cord. The butt plate is what the lower bolt snaps clip to and the bungee is what keeps the neck of the bottle pulled into the diver’s side. The top clip is simply a backup should the bungee give away. (See photo).
To make the best of this method, the stage can be rigged with a small clip attached directly to the neck of the cylinder with a few turns of the cord and a lower clip (also on a small loop of bungee cord) attached with a pipe clamp. Just as with traditional rigging, the position on the lower anchor point affects the final resting point of the stage, and the aim is to have the cylinder sitting parallel to the diver’s side with its neck – and the regulator – tucked into the area under his arm.
Once again, there are refinements that are made to the lower anchor point when two or more cylinders are to be carried – essentially moving the anchor point closer to the cylinder neck – but the basic starting point on an aluminum 80 is to have the anchor a little less than halfway between the tank’s shoulder and base.
One final point worth mentioning is that all the preferred methods of rigging a stage bottle, whether it is the traditional cave configuration or a more streamlined sidemount method, allow the clips to be cut off in an emergency. In other words, there are no metal-to-metal connections. Bolt snaps, even high-quality stainless steel clips, have the potential to lock shut. This is especially true in salt-water use, but I have had clips that have only seen freshwater diving “freeze” shut.
Being able to cut oneself free of a stage bottle (or camera) beats the alternative in my opinion, and this informs the best practice of attaching clips with something that a decent cutting device can make short work of.
The secret to the effective and efficient control of a stage bottle is thoughtful rigging and practice. If a diver starts out knowing what the stage bottle is to be used for – for example, whether it will only be used as a contingency or whether the gas it contains is an important part of every dive plan – and if that diver follows a couple of simple guidelines, carrying an additional bottle becomes second nature. After some practice, even carrying two or three will be quite easy. Clearing out staged gas after a dive, I have swum with as many as seven stage bottles, at which point there are some other little tricks that help, but the first step is always to rig each bottle in a standard and sensible way.
Good luck, dive safe, and if you are trying to swim with a stage bottle for the first time, practice in shallow water!