A lot of rectangular solids can be constructed using all solid heptominoes. The smallest edge must be greater than 1 to fill the piece with the hole. The second smallest edge must be greater than 3, because some pieces only fit a 4x4 rectangle. The solutions shown can be rearranged to solve the other rectangular solids.

2x6x63 (6x6x21) |
3x4x63 (3x12x21) |
4x7x27 | 6x6x21 | 7x9x12 |

2x7x54 (6x7x18) |
3x6x42 (6x6x21) |
4x9x21 (3x12x21) |
6x7x18 | |

2x9x42 (6x9x14) | 3x7x36 (6x7x18) |
6x9x14 | ||

2x14x27 (4x7x27) | 3x9x28 (6x9x14) | |||

2x18x21 (6x6x21) |
3x12x21 |

Like a woodpecker you can remove each single piece with a mouse click and then put
it back again.
At the top left corner you can rotate the whole solid.

A representation of the solutions using layers is also provided.