Azaqua CO2 bubble counter METAL ver.2 is a sturdy, robust CO2 bubble counter. The integrated non-return valve prevents water from flowing back. A 4/6mm CO2 hose can be connected to both sides of the bubble counter.
Filling is easy by unscrewing the top part and carefully pouring water into it, for example with a 1ml pipette
High pressure is also no problem for this bubble counter.
Read here: everything about adding CO2 to the aquarium