I have a 2009 Heartland Bighorn 3670RL. When I pulled the lever to open the black tank valve, nothing happened. I’m guessing the cable came loose and needs to be replaced or the valve is broken. I can see the the black tank in the basement and the cable appears to go under it. What is the best way to access and replace. I’ve also heard that this could be a very messy job and would love some tips and tricks to make this as painless as possible.