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You'e quite right. Recycled polyethylene (or other recycled plastics)can consist of a high percentage of degraded short-chain molecules which are more inherently unstable than virgin polyethylene. The addition of recycled poly to virgin stock can also increase the amount of fugitive catalyst in the plastic, which promotes degradation. Good quality virgin resin from a reputable manufacturer makes for superior products, as can be said about any manufacturing operation.
The translucent poly tanks used here may degrade rather quickly (less than 5 years - due to your latitude, your mileage may vary) by crazing from sunlight and cosmic rays. Enclosing them in wooden boxes or putting them in a small storage shed will lengthen their useful time considerably.