I just spoke with one of my local plants on the phone.
They would want to charge me a nominal fee, in the range of £20 for an IBC / £4 drum.
From speaking with them, the volume is of little benefit for them, and the charge was more to cover their man-hours in physically emptying the containers. Ie they were happy to take the waste, but wanted to make a nominal charge to cover their costing.
They did, however, want it packaged properly, and we talked sodium / potassium, and came to the conclusion that it would be best for it to stack up, and for me to drive it all over on a hot day in the summer, so it could be poured out.
Anyhow, assuming glycerol out == meth in, and that, without recovery, a drum of meth processes 1000lts of bio, that adds a cost of £4 / 1000lts to the process.
Which, i think, is acceptable : )