Apeks DS4 with a double bladder BCD

[Centrals]

only DST have 5 port

Apeks does say that the 5th port(AP0274) is ONLY suitable for DST and nothing else. But I had a look at the inside of both DST and UST and could not find any differences except the dry seal compartment which has nothing to do gas delivery.
I must be missing something.

 

[elan]

I had ideas of using a swivel or 3rd small tank for the drysuit

If you insist on using a dual bladder just keep the second bladder disconnected and orally inflate it when needed. The more inflation you have connected the higher the risk of auto inflation in that cold water. In the config you want to make you will have 3!

When we dive water that cold we usually disconnect the wing inflator and keep the DS connected only.

The wing is orally inflated. Not a big deal.