2006 Monaco Monarch SE 32 foot grey water valve cable problem

I own a 2006 Monaco above, which had the cable on the grey water valve pull out, ( grey water tank is half or more full)  I now have a tgrip handled cable with a metal wire straight on one end that it would seem was clamped onto the distal end, ( at the valve ) at one point, although it is so cramped I can't quite imagine how one would see the valve, much less replace it.  I have only been able to see the outside end of the valve head and can't see the whole thing, because it is so cramped with the other valves and the plastic bucket housing and the dash itself.  To reach it from the top would seem to require removal of the bedroom cabinets, cutting the floor to make an access panel then replace the valve as otherwise described here.  I have looked and don't understand how the distal connection with the bare wire was made.  I assume there was some sort of clamped hook that pulled and pushed the valve open and closed with the wire but I don't know how it was attached, if it can be reattached if it was accessible and what is recommended to get up there and do the job.  I use so little water when I am out that this problem might have been in place for a year and I did not know it. 
Any advice on a simple fix?  Or is coming in from the top to make access, the best way to make a normal repair.

I assume that if I don't do something eventually the shower will back up... but if the gray water somehow mixed with the black, ( it doesn't seem to) then I might not need to address it right away.  In short, the black water valve works, the gray doesn't and its a cable attached.  Does anyone have the voice of experience here.?

Welcome to the forum from California, It doesn't get any cheaper or easier than this.

https://www.etrailer.com/RV-Plumbing/Valterra/T58.html?feed=npn&gclid=CjwKCAjwxJnNBRAMEiwA8X_-Qdafb1ouOd6UuITv12EKhJDOuaQ73HhiycGDJB-Lg_ABKflVxCPEOhoC3i4QAvD_BwE

Don't know of a good fix for your problem, but at least it would be good for you to know how the cable (piano wire) is attached to the valve............assuming yours is a Valterra.  I had to replace the valve on my rig (nobody likes the cable operated valves, BTW) but access was no problem.  There is a picture of a 1-1/2 inch gray water valve on Amazon here:
https://www.amazon.com/dp/B00OA7Z14O/ref=sxts_bia_sr_1?pf_rd_m=ATVPDKIKX0DER&pf_rd_p=3182441022&pd_rd_wg=DNO9J&pf_rd_r=7Y98HG4MZFXE9Z0H2NC3&pf_rd_s=desktop-sx-top-slot&pf_rd_t=301&pd_rd_i=B00OA7Z14O&pd_rd_w=HSF2p&pf_rd_i=valterra+cable+actuated+valve&pd_rd_r=98JQH2J7GXY9PP580S40&ie=UTF8&qid=1504151685&sr=1

The outer sheath of the cable is held by the "squeezing action" of the screws in the plastic valve body extension there at the top of the picture.  There is a longitudinal hole bored in the center cylindrical shaft (the movable portion of the valve) there in the middle of the picture.  The movable "piano wire" part of the cable is inserted in that hole and held in place (well, it is SUPPOSED to be held in place) by a setscrew (allen head) drilled normal to that cylindrical portion.  (It is on the backside and doesn't show in the picture.)  If that setscrew was not torqued down real well at installation the piano wire portion of the cable could sure pull out (apparently yours has) especially if the valve gate itself became a bit harder to open over time.

No solution for your access problem........unfortunately.  If you could just "get to" that cylindrical portion, one might be able to smear some JB Weld on the piano wire with a Q-tip and get it into the hole, then later get it to at least open so you could re-plumb that drain pipe with a valve located elsewhere but it sounds like that can't be done. 

Hope someone with a rig like yours has run into this and had a happy ending.  Perhaps a post over on the "Monaco Owner's Forum" at the irv2 forum would yield some results.

Best...................  ed s