Slip unions are used when you have a need to take the pipes apart again. Like the couplings they are used to join two pipes together. However, unions have some special properties that allow them to be taken apart for repairs or for mobility. Once the pipes are connected to the two halves of the union, they screw together (without the need for the pipes to turn) and include a washer to provide a water-tight seal. Slip Unions are used when joining to two smooth pipe ends together. The male and female union sections cement or glue onto the smooth pipe ends and then the union is screwed together to form the joint. All of our Schedule 40 fittings are NSF rated 14 & 61, which means they are certified for use with potable (drinking) water. Maximum temperature is 140 degrees F.