So far, Rochester seems to bear it out.

IMO a simple split that you guys agree on would work best instead of trying to calculate a ratio of what your share should be. Are

I know what you're thinking...duh....but bear with me for a few more sentences. 

However; it seems that what you would need is a Licensed General Contractor/Remodeling Contractor, that can look at the space and tell you whether or not the walls you want to open up are load bearing, and a beam needs to be put in to carry the load, etc. 

I'd bear in mind that contractors who take CC are probably (or should be) charging the processing fees.

  $6200 later and that house has a brand new drain.Doing a bath remodel on my own house, realized I wasn't confident about beams to replace the bearing walls I was removing. 

When i spoke to the realtor he told me I can hire a company to test the soil around the tank.

You have to replace the total value with at least as much equity as you currently have, however, so bear that in mind.

@Jon S. Oil

I have worked with my attorney on the two L/O's I did in 2016, so please bear with the simplicity I use.