Bruce Brown wrote:
Also check the overflow. Many times if you fill the tank 100% it can hit the overflow, which will create a syphon and you'll lose a bunch of that 82 gallons.
This is definitely something to look into. When we first got our GBM (I was a complete RV newby), I filled the freshwater tank until water came out the overflow and stopped. Usually right before pulling out of the driveway.
Most of our first year trips were within 2-3 hours of travel so we didn't even usually stop along the way. On our first longer trip, I pulled into a rest area about 80 miles from home. As I exited the RV, a fellow RV'er told me that we're leaking freshwater! I checked, and sure enough, he was right. The dreaded "siphon problem".
My solution was to get a couple of shark bite shut-off valves and install them on the ends of the two over-flow pipes. (My rig has 2: one on each side directly behind the rear wheels.) Now when I fill up the water tank, when water flows out the drains, I close those valves. The next day, after some water usage, I'll open the valves and usually the situation is resolved. If water is still leaking, I'll close the valve and check again after we use more water.
With a crew of 2 adults, 4 children and a dog or two, I wanted to maximum our freshwater carrying ability.
So, definitely look into that possibility on your rig. It might even be fine when you fill the tank on a level, but upon travelling up/down hills, the water might slosh enough to get a siphon started.
Good Luck,
~Rick