3.2G RO water storage tank usually be used as built-outside RO tank for RO water purifier. The RO water storage tank are made of 4 main parts:
The inner most layer butyl diaphragm

The second layer polypropylene line

The outside layer metal sheet

The bottom plastic predestal

The water is stay between Polypropylene liner and butyl diaphragm.

The detail parameter of 3.2G plastic RO water tank:

Working pressure 10psi
Max working pressure 100psi