@farmerman,
This is easy. I am doing it now. I'm diabetic, and I injected water in one tube with an insulin syringe and resealed it a while. But you don't have to have needles to put water in a tube.
I had a huge old tube of DaVinci yellow ochre, and the water I put in the top leaked at the bottom. So I cut the bottom open and dropped the whole tube in a small jar of water a while to soften.
I scraped paint out t of the bottom of the tube and put it in small plastic pill bottle with a dab of honey and water and am letting the water evaporate.
I resealed the top half of the tube into a plastic baggie to keep softening it. Eventually, I will scrape it out and put in the small pill bottle with the rest. Or, I may let the top half harden in the sun and then the hard chunks will fall off easily.
It will all be sealed in the plastic bottle a while with dabs of honey and glycerin and more water, shook up repeatedly, left sealed, and then I will take off the lid a while to let the water evaporate.
Pan watercolor in a small recycled pill bottle! After it gets congealed at the bottom, it will be easy to put water on the top and just moisten the top layer and pour some out for a wash.