I have an overflow drain in the floor of my two bathrooms. The one in our ensuite seems to have an unpleasent odour coming from it. Its not offensive but enough to be distracting. The sink and shower and toilet in the ensuite all flow well. You can see water if you look down the pipe in both bathrooms. I was wondering if it's the smell of stagnent water or if the water should be there at all. The overflow drain in the other bathroom doesn't have the smell but that bathroom isn't used nearly as much. We are on a slab. Hopeing you can help would love to get rid of the smell.

Can you actually see water running down the drain if you look inside the drain with sink or tub running ? I hope not... :-). There are 2 options:

1. The drain should have trap installed below the grade. Trap prevents sewer gas from entering your house. If there is no trap, your floor drain became another vent for your sewer system. Solution is to either plug the drain and don't use it at all or break the concrete around the drain and install a trap.

2. This happens when floor drain is not too much in use. Water inside the trap evaporates and eventually stops preventing sewer gas from entering your room. The solution to this problem is to periodically use the drain. Make sure there is standing water inside the trap at all times. Make it a habit to pour a cup of water in it once a week.

In commercial applications, plumbing Code requires installation of so-called "primer". Simply said, primer is a cold water line attached to the trap below the floor level on one side and to the primer unit someplace on the wall, near the drain. Primer continuously drips water into the trap, making sure the trap stays wet and never dries up.