I've heard 1/4" per foot and I've also heard 1/8" per foot is acceptable for waste lines. What is the ideal slope? Does it depend on pipe size or fixture type? (i.e. toilet vs sink) Thanks!

I used sand mix (with acrylic fortifier) for the pre-slope I built for a new shower pan. After the mortar sets up(two days later) I checked the surface by knocking on it with a stick, I heard hollow ring instead of solid thud in some spots. What does this mean? The material in the spots where I...

If a line has an undefined slope, what can you say about the horizontal coordinates of each of the points on the line?

We have a 40 year old house in the country. Our washer drains into a 1 1/2" line through our home's back wall and underground for about 35 feet. Then the line runs out of the ground and out into the yard, terminating about 50 feet from the house, draining in the yard. Other older homes in our...