Sherwood Avid BC with Gemini Octo

A BCD should fit snugly enough that it does not ride up toward your ears when inflated, while still letting you breathe fully. Fasten the waist and cummerbund first, then adjust the shoulder straps so the tank sits close to your back and the shoulders cannot slide off. With the BCD fully inflated at the surface you should still be able to take a deep, comfortable breath; if it squeezes your chest, loosen it or move up a size.

Rinse the outside in fresh water and also flush the inside of the bladder, because salt water gets in through the inflator and dump valves. Fill the bladder roughly a third full of fresh water through the oral inflator, slosh it around, then drain it out through the inflator and each dump valve. Hang it to dry out of direct sunlight and store it partially inflated so the bladder walls do not stick together.

Integrated weight pockets carry the lead in the BCD itself, which many divers find more comfortable and easier on the hips, while a weight belt keeps the weight independent of your BCD. Either way, you must be able to release your ditchable weight quickly with one hand, and your buddy should know how your system releases. Non-ditchable trim pockets are useful for balance but should never hold weight you might need to drop.

Make sure the BCD is completely dry inside and out before packing so it does not mildew in transit. Remove all weights, deflate it fully, and fold or roll it around softer items such as a wetsuit to cushion the inflator and valves. Avoid hard creases in the air cell, and unpack and air it out as soon as you arrive.

Follow the service interval in the manufacturer's manual, which is commonly an annual inspection alongside the rest of your life-support gear. Have the inflator, dump valves, and bladder checked any time the inflator sticks, free-flows, feels rough, or the BCD holds air poorly. Between services, confirm that it inflates and deflates properly as part of every pre-dive check.

A jacket-style BCD holds air in panels that wrap around your sides as well as your back, while a back-inflate BCD keeps the entire air cell behind you. Jacket styles tend to feel very stable and upright at the surface, and back-inflate styles keep the chest clear and are often preferred for horizontal trim underwater. Neither is objectively better, so treat it as a fit and preference decision and try both if you can.

Most recreational BCDs use an adjustable cam band sized for common single-cylinder diameters, so standard aluminum and steel tanks generally work. Re-check the band tension after the first wetting, because webbing can relax slightly and let the tank shift. If you dive doubles or unusual cylinder diameters, confirm compatibility with the manufacturer before assuming it will hold.