The pile of bits for the waste oil conversion is growing...
This little lot, plus a large quantity of fuel grade rubber pipe should form the basis of the changover and purge systems. In an ideal world, I would have had two way valves, but two single valves seems cheeper... Turning them all off would probably be a pretty good anti theft device.
The current intention is to have a electric fuel pump for the waste oil tank, feeding a heat exchanger connected to the coolant, probably mounted on the passenger footwell. This will then feed into the main filter. Startup will be on normal diesel, switch to waste fuel once the engine has warmed up a little. Shortly before shutdown, the return from the injector pump will be switched to return to the waste oil tank, rather than the filter, and after a few minutes, the filter should only contain diesel again.
I'm not quite sure yet how I'm going to make the heat exchanger - I've decided a way of making pretty much everything else. In the short term, I may leave it out, and see how things go - I suspect it will run fine in summer, but I will need it as the winter draws in. A possible plan for the heat exchanger is a Series 3 heater matrix, sealed in a box full of oil, with an entry port at one end, and an exit port at the other... heat exchanger are avalable commercially for people running veg oil, but that would mean spending money. Its cost me over £50 for various fittings so far, so I don't want to spend a lot more until I know it all works fine.