Have RV Questions? Ask an RV Mechanic Online.
Hi my name is Robert...
First thing to do is check the vent on the roof, the tank needs to breathe to drain properly. The piping under the vent cap should be above the roof line, make sure nothing is under the vent cap blocking the piping.
What you can also do is put a back flusher on the discharge pipe and try to clear any blockage near the discharge valve. Most RV parts stores have them and you hook up a garden hose to it. It is also possible the valve failed and would need to be replaced. IF you run a coat hangar up the discharge you should be able to tell if the valve is opening or not as the hangar will go up the piping further with the valve open.
IF you get the tank pumped out you might want to dump several bags of ice down the toilet and fill 1/2 full and go for a drive sometimes the ice will push on any blockage and help clean the tank.
IF you have left the discharge valve open for a very long time please let me know, the reason being is the waste can backup and cause major problems. You should be waiting until 3/4 then dumping as gravity does all the work.....
Let me know if you need more help follow ups are included, IF you are satisfied with my efforts please feel free to select a rating, it is the only way I get credit for helping. Robert
Hi... Was just checking in to see if my answer helped??? IF you have more questions or concerns please feel free to contact me... Robert