The recommended slope for the horizontal run of sewer line is a miniumum of 1/4 inch per foot. When you look at diagrams of plumbing, you see vertical pipes meeting horizontal pipes with fittings that make a 90 degree turn. If things were set with geometric perfection, there couldn't be any slope on the horizontal pipes. So how is the slope implemented in practice?

Do people install pipes in the fittings slightly askew so the horizontal pipes can slope?

Or are the vertical pipes not set perfectly vertical?

Or are there nominal 90 degree fittings that actually make more than a 90 degree angle?