I do not like used plastic for storage unless I know everything about it. Plastic is porous, and you will get residue of everything ever in the container. Many people purchase food grade pails and barrels for storage only to learn that the soap residue in the plastic, even tho food grade, taints their food or water.
Are you a welder, or can you barter for a welder? Stainless steel sheeting in 4' x 8' is $270 per sheet for 16 ga. five sheets will give you a an 825 storage tank for about $2 per gallon after you throw in some bracing and fittings. A custom built tank in a cellar or crawl space, outdoors if you live in the correct climate, would give capacity and maintenance benefits that would far outweigh the restrictions of salvage containers or one size fits all kits in the survival world.
Keep in mind that survival needs are one gallon per day per person, so a three month supply for a family of four would be 360 gallons. My example above would meet the basic needs and then some for a family of four for half a year!