Roughly twice a month, a customer sends us back a tote that they claim "leaked" but which we cannot reproduce on the leak test in our bay. The first time this happened years ago, I was confused. The fifteenth time it happened, I noticed a pattern: every single one of these "leaking" totes had previously held a liquid that contained blue dye. Windshield washer fluid. Some industrial coolants. Certain fertilizer formulations. RV antifreeze.
Why blue is special
The dye in most of these products is a derivative of triarylmethane chemistry, and triarylmethane dyes are unusually good at penetrating HDPE at the molecular level. After a few weeks of contact, the dye soaks slightly into the inner wall of the HDPE bottle. From there it can slowly bleed out into whatever is filled into the tote next, even after multiple wash cycles. When that next content is a clear or pale liquid, the customer sees a faint blue tint and assumes the tote is leaking.
It is not leaking. It is bleeding. The visual is similar but the cause is completely different and the fix is completely different.
Why you cannot wash it out
We have tried. We have run extra-long hot-wash cycles, increased caustic concentration, and added a peroxide rinse step. We can usually reduce the bleed-out enough that you cannot see it in clear water, but we have never been able to fully reset a blue-dye tote back to a state where we would put our name on it for refill into a clear-liquid food application. The dye is bonded into the HDPE matrix and the only way to fully remove it is to replace the bottle.
What we do now
When a tote comes in to our intake bay with documentation that it previously held a blue-dyed liquid, we immediately route it into one of two paths. If the tote is otherwise in great shape (clean cage, good pallet), we re-bottle it — pull the old HDPE bottle out and install a fresh one inside the existing cage. The replacement bottle costs us about $58 and adds a couple of hours of labor, but it fully resets the tote. If the tote is not great structurally, we route it directly to recycling.
We never try to wash a blue-dye tote and ship it as food-grade. We have learned. The customer who owns the next refill almost always notices.
What to ask before buying
If you are shopping for reconditioned totes for any application that involves storing a clear, light-colored, or visually-important liquid, ask your supplier whether the tote's prior contents included any dyed liquid, and specifically any blue-dyed liquid. A reputable supplier will know the answer or will go look it up on the chain-of-custody log. We will, every time. The answer determines whether you should accept that specific tote for your specific use case, and the question costs nothing to ask.
— Aldo Ramírez, IBC Denver