Originally Posted by Joeyak
I just got this rv and the gray tank show 3/4 full when empty how could I fix this problem
Holding tanks usually use electronic conduction to "check" the level. The higher the level of the liquid, the higher the reading. If the reading is caused by something in the tank, the simplest way to address the problem is to flush the tank - using lots of water. Fill it up and go for a drive...maybe even find a bumpy road.
There a lot of buzz about the "GEO Method." Search on this forum or the Internet...there's lots of material.
Best of luck