I use a changing tent with BTZS tubes to switch from presoak water to developer. I just lay out a bunch of kitchen towels on the inside bottom of the tent just in case any drops of either presoak water or developer slips out. Very easy to use since all the water and developer empty into the cap anyway. Just turn the tube upside down, unscrew the cap with the water and then screw the cap with the developer onto the tube. Of course you would need 2 caps for each tube. From here on it is pretty much okay to move into the stop and fixer under subdued lighting conditions.