This has nothing to do with tubes but is a great way to develop large photo paper - I have used up to 20X24. I use a large clear garbage bag, costs next to nothing, and put the exposed paper in it so that it is flat on my developing table. The floor is just as good but not so comfortable. I pour in the developer, set the timer, and agitate with my hands over the top of the bag. When the timer goes off, I pick up the paper and bag by the corner, and pour into small plastic tubs, draining well. Then I pour the stop bath in, etc. I can increase development in one area of the print with the warmth of my hand. Try it

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foto phred