| Plumbers Union Local 12 Annuity Fund | Related tax-exempt org | Employee benefits | MA | 042621293 |
| Plumbers Union Local 12 Pension Fund | Related tax-exempt org | Employee benefits | MA | 046023174 |
| Plumbers Union Local 12 Education Fund | Related tax-exempt org | Training fund | MA | 046266388 |
| Plumbers Union Local 12 | Related tax-exempt org | Labor union | MA | 041106780 |
| Plumbers Union Local 12 Labor-Management Cooperation Trust | Related tax-exempt org | Labor management | MA | 046742981 |
| American Plumbing & HTG Corp | Related taxable corporation/trust | — | MA | — |
| ADAM Schindler Plumbing & Heating | Related taxable corporation/trust | — | MA | — |
| AJM Plumbing & Heating LLC | Related taxable corporation/trust | — | MA | — |
| Blue Bear Plumbing | Related taxable corporation/trust | — | MA | — |
| Boston Housing Authority | Related taxable corporation/trust | — | MA | — |
| Boston Mechanical INC | Related taxable corporation/trust | — | MA | — |
| Burns a H CO INC | Related taxable corporation/trust | — | MA | — |
| Cambridge School DEPT | Related taxable corporation/trust | — | MA | — |
| Cannistraro J C INC | Related taxable corporation/trust | — | IN | — |
| CARL-Louis & CO INC | Related taxable corporation/trust | — | MA | — |
| Clemenzi PLG & HTG | Related taxable corporation/trust | — | MA | — |
| CMP Plumbing & Heating LLC | Related taxable corporation/trust | — | NH | — |
| Collins William M CO | Related taxable corporation/trust | — | MA | — |
| Commonwealth Plumbing Corp | Related taxable corporation/trust | — | MA | — |
| Corcoran EDW F PLG & HTG | Related taxable corporation/trust | — | MA | — |
| Corporate Mechanical of NE LLC | Related taxable corporation/trust | — | MA | — |
| Deluca Welding | Related taxable corporation/trust | — | MA | — |
| Diamond Mechanical INC | Related taxable corporation/trust | — | MA | — |
| PJ Dionne CO | Related taxable corporation/trust | — | MA | — |
| DJ Plumbing & Heating | Related taxable corporation/trust | — | MA | — |