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Really liking the idea of an OTS container because it’ll be more reliable than 3D printing things, from my first look. Amazon link that I’ve been searching: https://www.amazon.ca/s?k=plastic+water+storage+tank+2.5L&crid=2XY0SQTAAPRKO&sprefix=plastic+water+storage+tank+2+5l%2Caps%2C149&ref=nb_sb_noss. Uline also a good place to look.
Tank requirements
watertight
able to install a pump/valve
lightweight
Tank nice-to-haves
baffles in the interior to prevent sloshing
Some COTS options:
https://www.uline.ca/Product/Detail/S-22889/Jugs/Jerrican-1-1-4-Gallon-Natural (4.731765 litre, 410 g)
must buy 4x at a time, 13$ each. 52$ base
https://www.uline.ca/Product/Detail/S-22920/Jugs/Square-Utility-Jugs-1-Gallon-Natural (3.78541 litre, 440 g)
must buy 12x at a time, 3.80$ each. 46.60$ base
Could install baffles in a COTS jug by cutting a slit into the side, pushing a flat piece of plastic in (about 50-75% of the way), and sealing the base of this piece into the cut exterior with epoxy.