Hi everyone
In the past I used LEGO pneumatic tanks as water container for my models. Like this it is possible to build working LEGO fire trucks with 100% LEGO parts. However, there may grow fungus in the wet pneumatic tanks since there is always residual water in the tanks after draining them. Therefore, I decided to create custom water tanks with my 3D-Printer. It worked quite well, and I was able to build a 100ml tank with the dimensions 9x9x5 studs and pin holes:
And it looks like this in action:
Cheers FT