Easier way in this video https://youtu.be/HZAVFpYvAoo

Learn how to fix non-manifold edges on a solidify modifier in Blender! This tutorial shows you step-by-step how to identify and resolve issues with T-junctions and intersecting edges, ensuring your 3D models are ready for boolean operations and 3D printing. Perfect for creating party lines for slip cast molds, this video will save you time and frustration.

00:00 Introduction
00:30 Checking for Bad Contiguous Edges
01:15 Fixing T-Junctions
02:40 Applying Solidify Modifier
03:00 Identifying Non-Manifold Edges
03:30 Resolving Overlapping Edges
05:30 Removing Interior Faces
07:30 Additional Non-Manifold Edge Fixes
10:00 Final Check and Boolean Operation