Grey tank venting problem

[jwhat]

I have a 2002 Layton travel trailer by Skyline. I am having a problem with the venting of my grey tank. The problem is everything is fine until I get the tank about 3/4 full, then the tank doesn't seem to vent and the oders start venting back up the kitchen and bathroom sink. The water will start to back up until I unscrew the undersink vents and let the pressure off the line. I am thinking the vent pipe come down to far in the grey water tank. All is ok until the water level gets high enough to block the vent pipe. I am working out of town and using the travel trailer and am not able to drop the tank at this time. Has anyone else had this type of problem? I would be thankful for any help or ideas.

[TandW]

Are you level?

[jwhat]

Yes I am level. I am working at an oilwell site and the only drainage I have is when the truck comes and pumps me out. They are scheduled to come once a week but I am having to be pumped about evry 4-5 days. Have a 35/40 gal. grey tank. Company pays for the pumping though. Good deal because they charge $85.00 per pump.

[TandW]

Is the rig new to you? Did the tank fill to full previously? Can you access tank top to ascertain if it has colapsed in. You have two options that are easy. You can let out the gray water onto the ground if it is legal in your area. The better and more conscienable way is to sluice the gray into the black if the black is lower. Good luck!!

[Ray,IN]

If you know the tank depth you can use a tape measure to calculate how deep the vent pipe extends into the tank. First measure from top of vent pipe to bottom of tank, then to bottom of vent pipe. DON'T drop the tape!