Here is a slick little trick for emptying gearbox oils.The millwrights at our plant have started using a shop vac wet and dry model to suck the oil out of the box .Seems to work good on all types of oil.So now we have this down patthe other issue,which has been long standing is when you call for a drain and flush what is the most effective way to flush the box.Iknow this has been talked aboutlots but never have Iseen or heard of a good tried and true method that is repeatable for any type of unit.I think the person who ever develops a method that all can agree on will be seen as a god

I have been reclaiming gear oils and cleaning systems for over five years . The process I use to flush the gear boxes is to use the same oil that is in the systems. I take the oils from the system and bring them into my mobile unit, were they are filtered to 1 micron and brought up to 150 degrees F. to dehydrate the water, by the time the oil reach this temperature it has been through the filters several times so the oil is clean dry and thinned to a point were run with a consistency of water. I then refill the gear box to above the full mark with this hot cleaned oil. What this does is thins the jelly like sludge on the bottoms and the inside walls of the gearbox. The oils are then drained back into the unit and just before the system runs dry it is given a final flush of hot clean dry oil.
The system is then completely drained. I give the oil a final cleaning and when the oil is cleaned to a 16/13/ ISO cleanliness code and dehydrated to less than 100PPM water. The oil is returned to the clean reservoir for continued use. The advantage of the hot oil flush is that no solvents, so there are no cross contamination issues, and a complete drain can be achieved in stead of leaving behind 5 to 10 % of the dirtiest oils in the system.
I have found that the hot oil carries out the bottom sediment better than solvent and the active additives that are adhered to the metal surfaces are not removed. Systems that I have treated in this way and returned to retreat years later are cleaner than the units given a conventional oil change, because the clean dry oil in put into a clean dry system, rather than clean oil being put into a dirty system that within a short time of start up is as dirty as the oil that was just changed.