After the insert is installed, in fig. 1 and 2, water is added in fig. 3. In fig. 4 and 5, the odor barrier oil ( made from vegetable oil ) is added which then floats at the top. The urinal is now ready for use. Fig. 6 shows urine entering the trap. The trap is designed to keep sediments from urine flowing into the pipe, which can cause clogging. Only water and urine flows into the pipe and down to the sewage.