Images wash out differently on diazo and dual cures vs. pure photopolymers. Diazo and dual cures melt easily while it takes a bit longer to soften a pure photopolymer image, hence dip tanks help out a lot. A fully exposed screen on a pure photopolymer will often need a pressure washer development set to fan spray and may need to have fine halftones hit quickly at close range (3-6") to open them up.
If you have slime on the inside of the screen it is underexposed and needs more time. The emulsion's ability to withstand full exposure for press durability and to obtain desired resolution often depends on the d-max of your film and your emulsion of choice. When rinsing the inside of the screen it only needs a light rinsing. If you are using a pressure washer, spray the inside of the screen at an angle of 20-30 degrees to the plane of the screen. Never spray at 90 degrees straight on or your 80-90% negative dot can be washed off with hydraulic pressure. If your image gets plugged with emulsion when dried, up your exposure time.
If you have image areas that won't wash out then check the dmax of your films. If you can see through your film in most cases the exposure light can get through as well and lightly expose the image making it difficult to wash out. The other time the image won't wash out is if the diazo or dual cure is past shelf life and the diazo has dark hardened. This can also happen if you store diazo or dual cure screens above 80 degrees for long periods, or the emulsion or diazo has been left in hot rooms above 80 for a week or more. One advantage of pure photopolymer emulsion and coated screens is they can be stored at 100 degrees for long periods with no ill effects. The emulsion also has far longer shelf life of a year or more, vs 4-6 weeks for diazo and dual cure emulsions once mixed.
