You can buy a plastic "hat' that fits on the toilet bowl to collect your stool. It's on Amazon.
Stool tests are a big waste of money unless you are dealing with a lab from a Third World country. The lab techs here just do not have the experience. It is commonly assumed that there is only a 5% accuracy rate. parasites do not shed eggs all of the time. parasites can also be in your blood, urine and sputum.
Learn to collect the specimens from the toilet with a plastic fork. Squish the stool against the side of the toilet and pull out anything that doesn't dissolve. Put it in warm water to clean it. If you need to preserve it, put it in a saline solution that you get from your naturopath.