John, been up this weekend and cut a 2" access hole in each tank on the face (near the top!!) opposite end to the drain/fuel take off, pumped out through a 1 micron filter so I could replace the small drain fitting with a ball valve an hose tail, pumped a load through the same filter for a while, will go next weekend now fittings are in place and set up my transfer pump and filter and give it some bouncy runs over breydon while the pump runs, then swap to other side and do it again, hopefully this will shift most of the crud.
Too well baffled to get the pressure washer in.