A quick and simple 15x15 tileset with several connectors, so that most tiles will connect with others with no noticable seams. From the top left going down:

1: Large Corner, Side and Center Tiles (top set of 9)

2: Tube Corner, Side and Quad Intersection Tile (bottom set of 9)

3: Tube Terminator Tiles, Single Tile (5 at the bottom)

4: Tube to Large Connector End Tiles (4 at top right)

5: Tube to Large Connecter Tri Intersection Tile (4 in middle)

6: Tube Tri Intersection Tiles (4 at lower right)