We buy it from Monarch Chemicals in IBCs..the chemical cost around £240 for 1000litres at full strength. (they have depots covering all of the UK)
The mix, as stated, is approximate. But spill it and your jeans look like the work of a hippy in 1969....all white patches.
We sterilise all the poly in decapitated IBC's shoving about 100litres into a two thirds full tank of water...it lasts for a few days of work.
A bottle of Domestos in 20L of water will be plenty strong enough. Scrape ALL detritus off the poly box, then scrub with the hypochlorite. Do not rinse it off as the trace of fluid remains active until it dries in the air and the extra time allows it to penetrate all the nooks and crannies....which you often don't see in poly between the beads.. the last ones at night we just weigh down with stuff set on top and after scrubbing leave them to soak in it overnight.
It is more efficient than scorching of wood.......although it is not suitable for smaller beekeepers due to cost of equipment etc (but associations could go down the route) hot wax dipping is how we sterilise wood now., 10 min at 160C both sterilises against both foulbroods 100% effectively and preserves the wood for up to 20 years.
Thinnish plywood warps in 160C wax however.....so they must still be scorched or soda boiled.