Installation

In Blender open Edit, Preferences, Get Extensions, then use Install from Disk and pick the manhole_generator zip.

Usage

1. Open the Manhole tab in the 3D viewport sidebar (N). With nothing selected, click the picture to pick one of the 39 designs, or browse by group, then press Add. You can also use Shift+A, Mesh, Manholes & Drains.
2. The card at the top shows the design, its size and face count. Surprise makes a new random fixture, Vary changes the current one a little, Colors picks new paint and enamel colors, Wear adds new rust, dirt, rain and leaves, and the arrow resets the design. The quick row below opens the cover.
3. The icon tabs hold every setting: Cover (shape, size, surface, material, lifting holes, bolts, hinge), Pattern (cast pattern, grate openings or tray infill), Text & Emblem, Frame & Below (frame, height offset, tilt, open cover, shaft, rungs, water), Street (ground, patch, curb, gutter, crossing, curb inlet, wall, downspout, puddles, debris, stencil), Wear & Paint and Parts & Export (part visibility, detail, real geometry or baked maps, Save Maps, Convert to Mesh, Make LODs).
4. Every fixture has its origin on the road surface at the center of the cover, in real meters. Each part is its own named object in the fixture's collection; the cover is separate so you can animate it.