Now to the cap.
Cut a piece of acrylic slightly larger than the top flange. Drill two 1/4" screws using the flange as your template.
Route it out and drill the remaining screws. Now tap the top lid. This will be you degassing output.
Trap your gasket material between your flange and lid and cut it out using a sharp utility knife.
Now glue your top flange.
Add your fitting making sure you use teflon on them to prevent leaks.
Here's what the finished product should look like.
Hope this makes sense and enjoy the hobby!
djfrankie