Originally Posted by klatu101
yes, it is very possible that there's a trapped air pocket in your tank, caused by how or where the supply line is installed to that tank,..... every Casita's 40gal. gray tank has that same problem, caused by where Casita attaches the supply line to the gray tank, their 40gal. gray tank tops out at 25gal,.....a very popular and useful mod among Casita owners is the "gray tank vent mod", after that mod my tank went from 25 to 41 gal........ that trapped air has to have a way to vent out of the tank, ...... if trapped air is your problem and if your gray tank is translucent(it may be black) it will be easy to see your water level and any air pocket in the tank at the time when your tank shows full in the shower, if it's a black tank you probably won't be able to see the level thru the black plastic,..... if you can't see the levels, look for where the supply line is attacked to the tank, if it's anywhere other than at the very top on the side of the tank, it will cause trapped air, because once the tank water level gets to the top of the incoming pipe then no more water can enter the tank, thus you have an air pocket from that level to the top of the tank,....
your problem may be caused by some other reason, but trapped air can certainly cause that problem.... its possible that that is a common issue with your model, and no one else has ever discovered it by doing the check as you did,......... anyway, a trapped air pocket is worth looking for and may be your problem......
one other thought,..... were you level when you did the check, if not level, then an air pocket in the tank could be caused by that and solved by simply leveling,... just another thought