To access the holding tank area you will have to remove the plastic port aft ceiling piece in the aft stateroom. At that point you can slide your head and upper body to get to the top of the tank. When I did my sending unit on my 2006 H38 summer of 2013. I flushed and re flushed the tank out prior to starting. I brought the tools that were needed, plastic bag and rags. When your in there you will have limited arm movement. I am 6'2" and was able to remove the sending unit. After removing it I was able to clean and scrub it to remove all dried on waste. Once it was cleaned it will move freely and you will have an accurate sending unit. Word of caution your arms will look like you were attacked by a cat when your done due to all of the fiberglass.