I recently went through the process of changing lubes, actually a couple times. Each time, I was faced with needing to empty my Lyman 45 lube sizer so I could start using the new lube. I placed a bucket under my bench-mounted lube-sizer, removed the sizing die, and then used a heat gun to heat up the body of the sizer. I then pointed the heat gun into the die opening as I screwed down the plunger. The process was a bit messy, but it did drain the sizer of all the old lube. The process was easier the second time as I've been moving to progressively softer lubes with each iteration. I made no attempt to save/re-use what I drained but contemplated un-mounting my sizer from the bench and attempting to drain the melting lube back out the top of the body into a container so I could save/re-use it. The disadvantage there IMO was not having the aid of the plunger to get things flowing.
I'm sure there's a better/smarter way to do this so I'd love to hear from others who have settled on a good approach.
Thanks in advance.