Sick and tired of the cable valves that simply are designed to fail!
I replaced the Black Tank Valve with a standard "T" handle Valterra unit. Only negative was I had to open the basement and remove a couple storage bins to open and close the valve every time I flushed the tank.
Then recently the grey tank valve stopped closing. So on the down stream side of the box under the RV I added 3" and 1.5" valves. That worked fine until I closed the new 1.5" valve for a couple days and discovered the cable valve I left open was leaking, GRRRR.
So I decided to eliminate the 1.5" valve and cut a access hole in the bottom of the plastic box. Then decided to simply replace the valve and have it MUCH more accessible than the one I had installed.
I eye balled where the blade/handle housing would exit the plastic pan and cut a hole and slid the new valve it. It's VERY easy to access along with the 3" valve now. I just leave the two extra valves open now. I used an Utility Knife with sharp blade.
As you can see the JackHoles ran the Gas Pipe right over the box's fasteners that is why I cut the access hole. Actually glad I did. I used 1.5" x .75" strips of plywood for backing to patch the hole. Used Permatex "The Right Stuff" for sealant.
First fix below in first pic.
I turned the 1.5" valve horizontal and leave it open, easier than patching back the ABS and eliminating it.