Sodium picosulfate is unfamiliar to most in North America. For all practical purposes it is the same as Dulcolax. Dulcolax and Sodium Picosulfate are the same 'core' molecule. Bisacodyl (Dulcolax) has an acetate group on each end that comes off almost immediately, and what is left is very irritating to the bowel wall. As a result tablets are coated to delay release of the bisacodyl for 5-8 hours.
Sodium Picosulfate is the same molecule, but with NaSO4 groups on each end instead of acetate groups. It is more stable, but the bowel flora 'snip' off the NaSO4 eventually, releasing the same molecule you have with Bisacodyl. Because this happens slowly, Sodium Picosulfate doesn't need to be coated, and can in fact be dissolved in water with some help. Typical commercial products contain 5 or 7.5mg of sodium picosulfate per ml, so the dose if usually just a few drops.
Boehringer-Ingelheim, who makes Dulcolax, also makes many of the Sodium Picosulfate products (Dulcolax SP, Dulcolax perles, Dulcolax liquid, Laxoberal, Guttalax etc).
While Sodium Sulfate (Na2SO4, Glauber salt) is a laxative in its own right, the amounts contained in a typical dose of sodium picosulfate are so small that they have no effect. Milligram for Milligram sodium picosulfate and bisacodyl are roughly equivalent.
Sodium Picosulfate is not FDA approved (it is a suspected Teratogen), so it isn't sold in the USA. It is sold in Canada as a component of Pico-Salax, which is effectively magnesium citrate and sodium picosulfate combined for bowel cleansing prior to X-ray or colonosocopy etc).