I get it from a school too (maybe prep 'palm' them off?)
Anyhow, its not too bad with temperature. I wouldnt use it in winter, but its way better than the tallow i also get, which is mid summer only.
I reckon (although im just guessing) that a commercial collector would make the effort for 4k litres, but maybe not one.
You could, of course, just try ebay?
Personally, if it were mine, id keep it and use it (assuming that wasnt loads of bother) but then my central heating here also runs on bio. Indeed, id be tempted to offer you some cash, but i just think i wouldn't be competitive with what you could get elsewhere.
Ahh, just looked at where you are - you know Dick Jotec will swap you for some of it? He is close to Kidderminster.