Originally Posted by etep571190
I don't understand why air would come up the drain. Well at least not enough to be noticed as a problem. ...
Objectionable odors can occur from the toilet under these conditions. Here's what happens:
First of all, your bathroom vent has to be equipped with a high CFM fan like a Fantastic Fan, Turbo-Maxx or other manufacturer. They can really move some air. In fact, these types of fans are the RV version of the attic fans you sometimes find in the hallways of homes.
The fan in the bathroom must be running, turned up pretty high and be in exhaust mode (most bathroom fans are already set that way to draw excess moisture out of the bathroom when you use the shower).
As in most RVs, the bathroom door is normally open when it's not occupied so the fan has no problem drawing air through the door's opening.
But when someone goes into the bathroom and closes the door, the fan now has a limited opening of about an inch or two between the bottom (or top or sometimes both) of the bathroom door and the floor (and/or ceiling) in which to draw air through- not enough to satisfy the air appetite of the fan. Due to the shortage of air, a drop in air pressure forms in the bathroom, but it's so slight that it won't even be noticed.
If the toilet is flushed while under these conditions, the sudden rush of water traveling down the pipe leading from the toilet to the holding tank forms a seal to prevent any odors from coming back up the pipe. However, once everything's gone down, there's nothing but air in the pipe and the small amount of rinse water now going down. With nothing to create a seal, the reduced air pressure in the bathroom causes the higher pressure air (and odors) in the holding tank to travel up the pipe and into the bathroom. This process stops once you allow the blade to close on the toilet.
There are a number of solutions to prevent this from happening but here are two easy ones. Before
- Momentarily turn off the fan
- Open the bathroom door