Just reading several posts about black tank issues, seems like there are several, i started a thread 5 months after we bought our Gateway myself, i was having, still are having trouble with my black tank valave not closing, or leaking when closed, i noticed it first when we were staying in sub zero temps out of necessity, not because we wanted to, anyway, since then,Feb of 2014, i have had trouble on and off, now all the time, i hve tried everything, including having the dealership look at the problem, all to no avail, using calgon and detergent, regular tank deodorizers, lubricateing cables, nothing works. I had to install an extra valve on the end of the sewer line just so i don't get a suprise shower when removing the cap to install the sewer hose.
We recently sold our home so are staying in the fw until we close on our new home next month, so, i flush the tank daily, using the external hose hookup and running a hose down the toilet, i can get the tank to drain with no problem but the valve will not close at all, i can flush the tank with it closed, solids and waste will drain, the bad deal, with the external valve shut, waste backs up and into the drain pipes for the 2 grey tanks, now my galley tank will not drain completly, shows a quarter tank all the time, i have run the calgon and soap down that tank as well as the bathroom grey tank, it works fine, just the other 2 giving me trouble. If i could find a diagram of tank locatoons i would cut the ccoroplast and check the valves and cables, one thing i forgot to mention is the black tank cable has a grinding feel when opening or closing and is very hard to open, it takes all i hve to pull the handle out and close.
Since my warrenty is way past the experiation date and the dealership said they couldn't find any problems it is on me to try and fix, along with a few other things they couldn't repair or didn't want to. If anyone has a diagram of tank locations for a Gateway 3500RE, please let me know.
Thanks