Use a 3mm quick-connect to turn the water from your supply line either on or off.
Conveniently connect different fittings to serve different functions. Use a 3mm to 8mm to connect your main water line to your Blumat carrot line. Fit a 3mm to 3mm quick connect to turn the water going directly into your Blumats either on or off. Adapt a 1/4" drip line to the Blumat 8 mm tubing - quick and easy with this handy connector. Later if you like, you can change either side and go to 3 mm, 1/4, or 8 mm.
These high quality quick connect can be implemented in a number of ways and are recommended for all watering systems to make your life easier.