It seems that I was wrong about doing your own plumbing in Mass. The Homeowners exemption is only about acting as the General and not about doing the actual work yourself. Altho I am fully able to do my own plumbing I will acquiesce and hire a licenced plumber. Its all about safety.

you sir are a gentleman.. good luck in your project..
come back if you have ANY questions..

Actually, it is all about MONEY, and the influence of the trade unions.

Glad I live in Virginia and not Massachusetts (or any state with similar regulations).

Can a home owner in Mass even legally replace a toilet fill / flapper valve / wax ring?

IMO

1. Permits and inspections SHOULD be required for actual plumbing installations / modifications. (To protect the public.)

However -- Where and how are the lines drawn?

2. As a example I have always done my own auto repairs including BRAKES, exhaust, timing chain/belt.CV joints, steering links etc. (Never pulled/replaced a complete engine -- just the head).

3. Does / would Massachusetts consider owner vehicle brake / steering repair a hazard to the public?

4. If the answer to (3) is "No" -- It would appear that Mass auto dealers / repair shops should maybe do a little arm twisting with their legislators. (Make some "campaign donations" wink-wink) to get equal treatment with plumbers. (Virginia dealers do NOT take note.)

5. Disclaimer -- I was a paying trade union member (not plumbing) for at least 30 years.

MA requires copper or cast iron drains for commercial work. NH allows PVC.
so, if you go to a small coffee shop in salisbury MA you will see all copper or cast iron drains. if you cross the state line into seabrook NH a small coffee shop has PVC drains.
these businesses can be next door to eachother seperated by the invisible state line. as i have said in the past.."no one who eats in the NH coffee shop is dying of the plague..

I also was for 30 years.

It's a strange situation to say the least. I moved to MA and bought an old house about a year ago. Have basically gutted it and am 90% done with the restoration.

The plumbing thing here is a real racket. I had to have the house re-plumbed from stem to stern. Unfortunately you're technically not allowed to do anything. Which makes no sense; you can do anything else yourself including all electrical work. Anyhow here are a couple things I've figured out to reduce plumbing costs:

1. First of all, have a second water line put in for your irrigation. The water cost is half of what it is when it goes back into the sewer, in most towns at least. The town charged me a laughably low amount to do this.
You can plumb out that line to your heart's content since it doesn't touch the municipal sewer, and the plumbing inspector has nothing more to say about it.

2. Second, even on your main "connected" line, you might as well do all the crude running of pipes and hoses. You just can't connect glue or connect anything. It's crazy simple to run Pex hoses and such, and you just have the raw ends hanging out where the plumber will need to connect them. Similar thing for PVC pipes: you're not allowed to glue anything, but you can certainly cut the pieces and rough out what's what -- not like the plumber will follow your lead unless he agrees that you've got it right, but if you do it's just that much less labor cost. No need to pay to have dumb things like pipe hangers and stuff installed as long as you do it correctly (in our neck of the woods, you basically just have to use a lot of hangers and everyone's happy!).

The thing I can't quite figure out how to beat is finish plumbing, which is so easy it's basically a joke. I went ahead and connected up a couple of fixtures and got really yelled at by the plumbing inspector but he grudgingly signed off on it. I just needed one working bathroom and couldn't find a plumber, and it's child's play to put a knob on the shower valve, screw on a shower head, hook up the drain to the tub and connect up a vanity sink so I just went ahead and did it. It's really ridiculous that they charge $200-300 per fixture to do finish plumbing when it's so bloody easy.

In theory you can get fined $2500 for doing your own plumbing but if you have to do it in a pinch and have a modicum of interpersonal skills, you can probably get it approved without setting off too many alarms.

(The absolute key, of course, is __getting it approved__. It's utterly stupid to do plumbing work that isn't ultimately signed off on by the inspector, because your insurance company may very well deny coverage in the event of a problem.)