The following is my method of how to assemble you doubles. Doubtless there are many ways to go about doing this, but this is how I do it. These instructions cover Scuba pro, DiveRite, Sea Elite and the new Genesis manifolds. I have no idea how to do OMS or other lame manifolds.

First screw in your valves. I use a bit of spit (er, oxygen clean spit) to lube the valve O-ring and then tap the valves tight with a rubber mallet using the manifold side of the valve. Do not beat on the handwheel.

You need a flat, stable work surface to get your tanks together. I think a WorkMate is perfect for this task, it has plastic stops to keep your tanks from rolling off and you can open the middle to get at the lower band bolt.

Pictured here are 104's with a scubapro manifold.

The manifold has a "left" and "right". Test this by screwing in the manifold into one of the valves to make sure you have it oriented correctly . If you don't, it won't screw in when the time comes. If you have to, mark the correct side up with a felt-tip or piece of tape.

Set both your tanks on the workmate facing upwards and align them as parallel and flush to each other as possible. Use some lead weights to hold them in alignment. You can stick the O-ring extension of the manifold into the valves to help you align the tanks.

If you like you can use a straight edge to help out. Note the distance between the tanks at the shoulder, then look at the bottom of the tanks and make sure you have the same amount of separation there. Take as long as you need to get the positioning as correct as possible.

Once you get your tanks more or less in alignment, gently push the right valve valve towards the left while slowly rotating the manifold clockwise. You must do this carefully, immediately backing off if you feel undue resistance.

What you don't want to do at this point is to cross-thread the manifold or the valves, because if you do, you are screwed. Keep turning the valve back and forth while gently applying pressure to the valve. It should only take a turn or two for you to feel the threads engageing. If the threads are not engageing then you need to re-check you preliminary tank alignment.

If you did muff the job and cross-thread, God help you and break out your checkbook. If you happen to have a set of diamond files you might be able to dress the manifold threads if you are skillful. There won't be much you can do with the valves unless you can find a tap to fit the threads. Good luck with that, as the chances of your finding a left-handed fine-thread .625 tap is right up there with with an ice cream cone in hell.

But don't let me scare you, if you are slow and careful, you will do OK.