depends on scenario...if it's an existing rcp or vcp line and we can let concrete set overnight,...we'll hand dig underneath the pipe 8" deep, 6' diameter, place 3-8" block side ways 120 degrees apart so center of block is at 4' diameter, order bottom section of manhole with no bottom. set bottom section pour your concrete around your pipe...by leaving pipe in place, your invert is already there. next morning, saw out top of pipe and set the rest of the sections.
if it's a pvc line with little flow that's easily by pass pumped...we'll order our manholes with bottom, pre poured inverts and boots. saw out about 8' of pipe (4' each way from center of manhole, set manhole, run new pipe with pvc repair couplings (gasketed, no center stop)...into the boots, tighten...backfill.
slicker'n snot on a doorknob