Here we have a DS4 first stage with a Tx50 second stage rigged on an 40 cuft deco bottle. Notice that the 40" hose is routed to the left of the handle. That makes it easy to deploy and stow the reg on the bottle.

The 21 on the side is the maximum depth (MOD) for the bottle, 21 meter. So there is probably 50% nitrox or 50/25 trimix in there. There is also another 21 on the other side of the bottle so you can see the depth no matter how you hold the bottle.

As you can see I also have the second stage placed high. If you carry many bottles it's usually better to have it lower on the bottle since it has a tendency to be quite busy around your left d-ring otherwise.

If we look closer at the reg we can see how the SPG is bent back on a short HP hose. It's held in place with some cave line. On a DS4 it is best to put the SPG on the left so it is protected by the valve and the first stage.

You can also get a glimpse of the analysis tape on the right side. That is where you want to put it so you can view under water if you like to double check. The large MOD is what we use as our primary identification of the bottle.

This is a picture of a DST first stage an a small aluminum 30 bottle (perfect for oxygen in the ocean). Here we have to put the SPG on the right because it is a swivel reg. Anyway it is still protected since this first stage is larger than the DS4.

With the swivel first stage you should use a regular 36" octopus length hose. You don't have to of course but with a 40" hose you don't need the swivel and could have used a DS4. The DS4 first stage is by the way what I recommend.