Black tank vent clogged

[Rick and Mindy]

Long story short.......I have reason to believe my 31SL black tank vent is clogged. I have a redwood diagram showing a vent stack for each tank which would mean 3 stacks on roof. I only have 2. Wondering if the joined 2 tanks to 1 of the 2 stacks i have and which 2 tanks did they combine. It would make sense for the 2 gray but i have found that sense doesnt always mean anything. Has anyone else had this problem? How many stacks do you have? And how did you unglog the vent?

[XCMARK]

2 stacks , 3 tanks

when our black tank is almost full it burps as you flush.

[Cheezy1]

If your tank burps when flushed, you could have pyramid forming in your black tank. I would flush a couple of gallons of water mixed with a half a bottle of Dawn dish washing detergent down the toilet. Then fill the black tank up and leave it sit a couple of hours. Open the black valve and watch to see what comes out. Rinse and repeat if needed. To check your tank vent piping remove the roof cap and push a garden hose down the pipe and see if you can get to the tank. If you are really brave turn on the water and see if water comes out of the black tank drain. Be sure to have someone help you turn on the water and monitor the underbelly around the black tank to make sure that water isn't leaking from the vent to tank connection as they are sometimes not great. Good Luck!