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 a more 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!