I flatted the front wheel going up a climb the other day - I heard the pop and the PSSSSHH, and I could see a geyser of pale "steam" or vapour coming out the puncture.
I swapped out the tube for the spare and continued, but noticed the tube was wet inside the tyre. It hasn't rained on my bike for months.
When I got home I patched the tube, and noticed a lot of dampness around the hole. When inflated it bubbled like a mud pool. The tube also felt squishy and I couldn't push all the air out when stowing it later.
I guessed there was some water inside, so the tube was left hung up with the presta valve at the bottom and unwound.
The liquid was runny not viscous, and was clearer on top with the colour sunk to the bottom. The coloured bit looks like mud, or a suspended powder
The tube is labelled as "CST 700c 19-23" and a long number There is no mention of any sealant or puncture resistance to this tube.
Why does my tube have brown liquid in it?
EDIT: I removed the valve core and tried to purge the goop using a rolling motion. It didn't work so I junked the tube. I cut it open to see what was blocking the open valve, and it looked like this:
TL;DR? Squishy tubes are bad - buy a new one.