With a level
1/8 " - 11/2".
One quarter inch per foot is standard "slope". This equates to a quarter bubble on a level. If you don't have at least one eighth of an inch "slope", your drain will not work properly and will clog constantly.
You need at least a 3 in. pipe -- shower is 2 in. pipe
Only if the people want the contents to flow back or forward.
It needs aleast a 2 in. pipe. tubs are 1.5 in.
All you have to do is add a "Y" pipe or Call a plumber
1 in 150 for each pipe is better
One-quarter inch per foot is both the standard practice all around the country and the minimum slope (or grade) allowed by most codes. If maintaining that much slope is a problem, an exception can be requested from the administrative authority.
Radio Shack "drain pipe tracer".
If your thinking of sleeving the pipe it is not a great idea..Ideally replace the defective piping as drainage systems are designed by fixture units and reducing the pipe can cause major problems
No. If you think about it, upstairs toilets actually drain through the walls and down under the foundation and footings, so you would have a 100% slope there. You can have too little slope, but never too much, since gravity is actually what drains a toilet. Yes you can. Pipes that run vertical are not a problem because friction is not acting on either the solid or the liquid matter. Where a pipe is sloping steeply the water can run away leaving solid matter behind.
$8,300