Terrible smell and pressure from second toilet
we have a 99 Forest River Cardinal 5th wheel which has a the second bedroom with a toilet. While the master toilet works perfect, the second bedroom toilet has a terrible smell.
When flushing, pressure is coming backwards from the tank, spraying all the dirt to the toiled lid and seat.
Common sense tells me that this must me an issue with a clogged vent. I went up to the roof but only see one vent at the toilet. I put our shopvac in and can hear it sucking from the sink and toilet, indicating that it seems to work. There is a second went on the roof in back middle. Opening the vent lid I can only see insulation, what is that vent for ? Is there any other vent of the black tank ? What else could it be ?
Last but not least, the external flush does not work. I checked the valve and it is not backwards and water is coming out when unscrewing the pipe there, so this seems to work.
Thank for any help