I thought that I would offer this to those who may be entertaining moving away from tray development of sheet film. I recently built BTZS type tubes for both 4X5 and 8X10 formats. The details listed below will be the same for both with the only difference being the size of the tubing and fittings. I use 3 inch for 8X10 film and 1 1/2 inch for 4X5 film. The tubing must be either ABS (black) plastic or Gray PVC (electrical) tubing. White PVC will transmit light and will not work for purposes of these tubes. The tube is assembled as follows. Cut the appropriate length of tubing that will allow 1/2 inch of film to be exposed after allowance for the fittings. This exposure is designed to allow easy removal of the film following processing. The fittings on the first component consist of a cap on one end and a "male adapter" on the other end. These are glued on to the tube after both surfaces are cleaned with Acetone and then glued with appropriate cement. The second component is assembled from a "waste adapter" and a "male adapter" of the appropriate size. These are cleaned as before and glued to each other. The "waste adapter" is a male slip (glue) X "female pipe adapter". The third component is assembled from a "waste adapter" and "cap" of appropriate size. The cleaning and assembly are as before. The fourth component is a piece of fiberglass window screen material cut to a size slightly larger then the film format size. The manner in which this tube is used is two fold (gentle agitation and minimal agitation). In "gentle agitation" I place the third component with opening up and fill it with the appropriate developer. I then (in darkness) remove a sheet of film from a holder and place the piece of fiberglass screen on the backing side of the film. I gently bend the film and screen to allow insertion into the tube. The tube with one end still open is then placed into a water bath for presoak(I presoak for 5 minutes). The screen allows the water to access the antihalation layer of the film. After five minutes I dump the water from the tube and turn the tube so that the open end is down and screw this into the cap filled with developer. I then turn the tube over and place into the water bath container. I turn on the room lights. In gently agitation the tube is gently spun in the water bath. When it stops bobbing it is spun again. After the development time the room lights are turned off and the cap is unscrewed. The developer is poured into a collection container. The next step is to pour stop bath into the tube to the top. After 30 seconds the stop bath is poured from the tube back into the stop bath holding container. The film and fiberglass screen are removed from the tube and they are placed into a tray with fix. The room lights may now be turned back on. After appropriate fix time the film is then placed into the wash. In minimal agitation the second componant is added to the tube before the cap is installed in order the film is capable of be totally covered with developer. The tube is filled with developer rather then just the quantity that we used in the first method. For details on minimal agitation, I would recommend visiting the Azo web site. The benefits of minimal agitation are enhanced local contrast and greater sharpness due to "edge effects". I have found even development, no film damage and the ability to develop different sheets to differing contrasts at the same time with this method of development. I had used "brush development" to this point. My results show equal evenness of development using tubes.