Question 798651
{{{slope=(y[2]-y[1])/(x[2]-x[1])}}}
where the {{{x}}} is the horizontal distance (in inches) to the sewer main,
and {{{y}}} is the height (in inches).
We can make point {{{P[1]}}}({{{x[1]}}},{{{y[1]}}}) the connection at the main,
and {{{P[2]}}}({{{x[2]}}},{{{y[2]}}}) the connection at the house.
 
{{{slope=(-6-(-18))/(48*12-0)=12/48/12=1/48}}}
That tells us that going from the main to the house the pipe would go up 1 inch as it goes forward 48.
Since {{{1/48=about0.02}}}= 2%, maybe they call that a 2% slope.
Or maybe there are regulations for slope of the sewer lines, and maybe they measure the slope in inches per foot, so that would be
{{{12inches/"48 feet"=0.25}}}{{{inch/foot}}}