If they needed to re-shoot the scene and wanted more 'flow' they would refill it and shoot (pardon the pun} again. When it was squeezed at the base of the penis by whomever was grabbing, a stop valve was opened and the placebo cum was released at great force. The internal bulb held up to 6 ounces of a water powdered sugar/sometimes coke mixture. This also helped them maintain the erection without being 'fluffed' very often. This may sound a 'bit disturbing' but they have been known to insert a catheter type tube with a bulb deep in the mans penis.
