George, how old is your vacuum pump? It looks terrible inside with all that rust. It shouldn't hurt the operation of the pump but boy does it look yucky.
Tim.
Hi Tim,
Is not how old the pump is but, how many hours of work does it has...???
Age is about 20 months, oil consumption so far is about 4lt gallon container (oil changes), gallons of Cactus Juice put through, not really sure but about 30 gallons or so, maybe more, I have to ask Curtis...!
The pics are from my first oil sump removal and after the first 6 months of stabilizing gallon after gallon, I never had/worked with a vacuum pump before, I wasn't sure how often the oil should be changed (was clear oil, originally) and most importantly, I had no idea of how much moisture these pumps suck
so, I kept wondering why the oil level would go up and not down, to be point where, on releasing the vacuum, my primary filter (I had 2 at the time) would get full of oil...!
All that rust was created from the amount of water set on the oil sump for some time, the surface rust was easy to remove, even easier with my mini sand blaster, I don't think that I took pics of it after cleaned (I should have, tough..!
) but, it would never cause much damage as oil was running over all surfaces when working.
The sediment/gunk seen inside the sump, is a combination of various things, the water staying that for that long, was one of the bigger ones...!
The pump itself was rinsed with some degreaser and the motor turned on for about 10 seconds or less, that was enough to let the degreaser run though the system and wash out any gunk from the inside but, it come out fairly clean, all gunk was in the sump's bottom.
Since then, I only had to dismantle it once more after I decided to attempt dye (not stabilize) some timber I had, with a synthetic dark blue dye and 1 gallon of Methylated Spirits, not a good idea, I'm telling you, the vapours almost destroyed the pump and the new oil (red in colour) turn to almost black in less than 5 minutes so, that was the end of that, and a big mess inside the pump...!
I now maintain the oil level just above the minimum and strain/bleed the water on the sump bottom, by unscrewing the bleeding screw, until I get clean oil coming through, top up any oil lost in the process and keeping doing this before I turn the pump on, for every 8 to 10 stabilization session. Remember that my chamber is 16lt capacity, and I try to fill it as much as I can, each time, the amount of juice require to top it up, can be between a full gallon and a 1 1/2 gallons, this mean that, the double stage pump works a lot harder than most, 16lt volume to put and maintain under full vacuum for about 4 to 6 hours, is not an easy task so, oil changes have to be proportional to the amount of hours and load/vacuum required from the pump so, is no such thing as a set rule...!
Cheers
George
Drain the oil and remove the sump reservoir/cover, 4 hex bolts hold it together with a round O'ring as the gasket. This is a easy process and does not affect the pump in any way. There will be lots of gunk at the cover bottom, that you can now access easily and wash it all with petrol, 
the glass oil level window is now a lot easier to reach, the perforated metal cover is fixed/glue on the inside but, you can easily clean the glass (I use the air washing gun with some petrol in it).
you don't have to dismantle anything, you simple clean all that the best way you can and then put the cover back in.