Level of waste in the holding tank?

[Just Limin']

Is there a better way of judging the level of waste in the tank? I try to determine the level by opening the engine cover and taking a look. The interior of the tank has gotten discolored and I'm not sure where the water stops?
A gauge would have been a relatively inexpensive item to include....

 

[trailertrawlerkismet]

I made a post a while back on this very subject and it received a number of ideas and suggestions. Do a search under "Black Water Waste Tank" for further info in addition to what may get posted here.

Jim F