Found a possible large volume fermenter. Pondering, is it safe to use?

I found a large plastic container today at the recycling center.

I am wondering if it will be safe to use as a possible primary fermenter for 10 gallon batches.

Here is what I know.  It is thick translucent #2 HDPE plastic  and holds about 15 gallons (it has markings up to about 3/4 of the way and the final volume is 12 gallons/ 45liters) and formerly held an acid based CIP sanitizer.  The sanitizer was for the dairy industry it appears.  It is a phosphoric/sulfuric acid based sanitizer called fc-298 made by IBA inc…  It has a handle on top and a main cap and a vent cap on top.

So, it would seem to me that if I were to rinse it well with water a few times, perhaps take a pH reading of the final rinse it is feasible this will be safe to use?  Can anyone think of any reasons not to use this?

I have never been one to ferment in plastic but I brew 10 gallon batches at times or have 10 gallons of cider so it would be nice to have a one large fermenter rather than 2 5/6 gallon ones going.

Or maybe if not a fermenter it would be a great water collection vessel?  I get my water from a roadside spring and am constantly scrounging around for every empty bucket or keg I have to maximize my collection capacity.

Any thoughts out there folks?

Sláinte Mhath!