The 3" TC cap included with your BME Chronical has a 1/2" blow-off fitting and a pressure release valve, essentially you need a create a reducer fitting that goes from the lid cap's 1/2" blow off barb to your CO2 regulator's 3/8" OR 5/16" output barb.
There are two ways you can make an adapter to use it as a pressurized transfer fitting:
The first solution utilizes threaded fittings, see picture below.
1. You will require a 1/2" barb to 1/2" FPT threaded fitting to make the connection to the lid cap. That is available here:
2. Next, you will need a 3/8" barb to 1/2" MPT threaded fitting, which will thread into the fitting above, and make the connection to your CO2 regulator. Be sure to use Teflon tape for an air-tight connection. You can find that fitting here:
For those that want to utilize sanitary TC fittings throughout, you can create the same type of reducer that can be easily disassembled and sanitized. Furthermore, this may be an ideal solution for those users that have a non-traditional CO2 regulator output, such as 1/4" or 5/16" instead of 3/8".
1. Select a size for your CO2 regulator's output, such as 1/4", 5/16", or 3/8". Then purchase a TC hose barb flange in the size you ultimately settle on. Such as this one:
2. Then go ahead and buy a 1/2" TC Flange barb to rig up to the 3" TC blow-off barb, such as this one:
3. Lastly, pick up an extra 1.5" clamp and gasket to secure the two flanges together.
You have essentially created a custom TC reducer barb.
For both solutions, run a length of tubing from your regulator to your 5/16" OR 3/8" hose barb, and then run a length of 1/2" tubing to your BME's blow-off barb to the 1/2" barb on the reducer fitting.
Most importantly, both solutions enable you to avoid changing lid caps that could risk oxygen exposure!