[A/S] Thetford Blade Valve Replacement

[jclos@xxxxxxxx]

Group,
I have almost everything done, or know how I will finish, the pan 
replacement over the black tank.  I am fixing the leak that has caused 
the problem.  I removed the blade valve that is attached directly to 
the tank.  I got three of the 4 screws out fine using vice grips.  
They were so rusted that nothing much was left of the heads.  The 
fourth one, naturally, broke off.  There is a little nub of it 
sticking out.  I think the inside of the tank that these screws were 
in is made of some kind of plastic.  The outside is covered with 
fiberglass.  I filled the tank to make sure it was not leaking 
anywhere else, and this seems to be the only leak.
Has anyone replaced this valve?  I couldn't seem to find a replacement 
that would fit the 4 screw pattern anyway, so I was thinking of 
glue/welding a short piece of drain to the tank.  I could then mount a 
new drain valve that pulls open from the left or right instead of the 
top.  Has anyone else done this?  Thanks for any 
information/suggestions!
Joe