OK, clearing this up. yes i can build pressure with the mityvac and yes it takes too many pumps. i didn't have an air leak so much as an unrealistic expectation about my ability to build vacuum in the bucket's volume. i could have finished the job but my bucket was collapsing after a couple of hundred pumps, at about 5 inches hg. since so much absolute vacuum is needed (h/t funola, vstech), it seems a metal drum is called for, whatever the source of the vacuum.

thought experiment: anything else productive to do with bigger vacuuim reservoir in the trunk? maybe provide a vacuum wand for the interior?

I use a Tempo Oilboy. It used to be the most common extractor on the web, but no longer made. It's similar in design to the Mityvac extractors, but can't reverse to fill by pressure. It only holds 4 quarts, so I have to do two pulls on my 190d. To store the tubes, which are messy after use, I soldered a cap onto a length of 3/4 inch copper plumbing pipe.Hang it or lean it against the wall and there's no mess.

A 20 pound propane tank sounds like the perfect solution, no?

I'm pretty sure they are threaded 3/4" NPT which would allow almost any imaginable fitting configuration. One connection to attach a vacuum source for pulling the reservoir down, another for the fluid connection, and last how about a Schrader valve to add air pressure. That way you could pull vacuum, suck oil and then blow the used oil out to empty the tank if you stand it on its end.

Probably need a valve for each of the connections or the Schrader will leak when the tank is pumped down.

They sell dual valve threaded connections valves that have a dip tube to remove liquid or vapor... Ac recovery tank valves.

Kind of heavy to lug around?

Actually why have a vacuum tank at all? Once you create a siphon the oil should just flow into a shallow pan if the oil level is above the pan level. To get more height, put car on ramps. Only need enough vacuum to create the initial siphon. Maybe about 1 or 2 ft of oil or say 2" of mercury should do it.

Even with commercial vacuum extractors, they work best if put on garage floor so that oil level is lower than sump level.

On the other hand, could forget about vacuum. Just remove sump plug and let oil drain out by gravity ;)

Bookmarking topic for reference. I need this method of crankcase extraction for most of my engines these days.

this is what i expected to happen the first time i tried, but i couldn't figure out how to start the siphon with the mityvac. is that possible? i didn't want to put my mouth on the tube nor run oil through the pump. does it just come down to pulling the tubing off the barb at the right moment?

My mityvac came with a small, 250ml??, bottle which I've use for brake line purging and other lite suction duties. I guess you can use one or two plastic hose clamps to prevent oil getting into the pump.

Oil is pretty thick. Siphon may not have enough suction to overcome adhesion.

I've used this method to drain excess transmission oil. You can draw the oil into the tube with the mityvac, pinch the tube while you disconnect, and put the end of the tube in a pan and release. It does work, but takes a few tries to get it right. And the oil has to be hot.

Yes, getting oil hot would be required. It speeds things up a lot even when using the Mityvac vacuum extractors.

I haven't tried using the hand pump, but I guess you would need a valve of some sort. to allow the pump to be removed before oil gets to it.

But really - a proper vacuum extractor is cheap. So is removing sump plug. So unless you just enjoy messing about with dirty oil, why bother :D

MMMMMM...

http://4.bp.blogspot.com/-UOLAgoye5Z...lack+teeth.jpg

if this approach works, how to avoid sucking old oil into the vacuum system pump upon depressurizing an already slightly oily tank?

I use two connections for the tank... One NEVER sees oil, so no contamination from the dirty oil.

I think you meant you use two tanks in series, the main tank and another small safety tank.