Camelbak reservoir drying hook
thingiverse
Camelbak charge ten English pounds for a piece of plastic to hang the bladder and keep it open for drying. This thing does the same job, but you can probably laser cut it for about a tenth the price. The square notches wedge in the opening of the reservoir. Tested in 3mm acrylic and it works fine, but 5mm would probably stay in place even more easily.
Download Model from thingiverse
With this file you will be able to print Camelbak reservoir drying hook with your 3D printer. Click on the button and save the file on your computer to work, edit or customize your design. You can also find more 3D designs for printers on Camelbak reservoir drying hook.