Well, I didn't read the whole thread but if you have low pressure and are getting some pipe banging I can almost guarantee its a loose pipe somewhere. Long story short I've been in my home for 15 years. Always had pipe banging whenever I would shut off a tap, regardless where it was. My pressure is about 65psi so I installed hammer arrestors everywhere. No difference at all. I also have the air gap pipes but they made no difference either. A month ago I was replacing a bathroom faucet and noticed the pipes coming into the cabinet were loose. I could move them several inches. I checked the other water supplies and low and behold same thing, even the toilets! I took some expanding foam and sprayed it around the pipes where they enter the cabinet. I know its not ideal but I'm not removing cabinets and drywall to secure a pipe. The foam expanded, dried and essentially secured the pipes. I did this on all the pipes and my plumbing is now quiet as a church mouse. I lived with that for so long and all it took was a $5 can of Great Stuff to fix. Tell your GC to fix it. Its his problem not yours.

As an example, in the master-bath line, my apartment is the only one on our side with a flushometer. When we flush, and only when we flush, there is big banging up on the top floor. The plumber called from the top floor and had my DH flush our toilet while he was listening, so there's no question but that it's the flushometer. And it doesn't happen for the other toilets. So it's the large volume of water from the flushometer. I'm assuming water hammer. Would it be anything else? Apparently the noise of other toilets filling isn't really an issue. The walls are pretty solid; you'd have to be IN the bathroom to hear your own toilet filling, so I would imagine you'd have trouble hearing other people's toilets in our building. Hence the proposal of making us replace our entire toilet w/ a tank should our flushometer break. breaks. Brickeyee, about the arrestors: Can I put one above my toilet, on the cold-water supply line? Or does it have to go all the way on the top floor? I can get into my wall above the tile without a lot of pain, but the top-floor tenant can't do that without messing up her floor-to-ceiling limestone-covered walls. I would have assumed that in her renovation, her architect & plumber would have put the arrestors in along with all the new pipes. I haven't been able to find out for sure when this got bad enough to become an issue; she would probably tell me it has always been like this. Whether it has or not.

You might be able to install arresters on your line if you share the same water lines with that neighbor and it will help some. Basically the pressure travels through the pipe till it finds a place to go, and if it travels up towards you it could be why you hear the loud noise. I had a toilet that when the fill valve stopped I would get a knock that sounded like it was coming from the main shutoff valve mutiple rooms away. I installed a water hammer arrester there and have not heard the noise since. I do know you are 'supposed' to install these close to the problem fixture, but I didnt have access to the line inside the wall by that toilet so I just installed it where it was knocking and it worked. I would try to locate where the noise is coming from and install them there on your lines

I did check that, and the documentation is very sketchy. Duravit #225010 http://pro.duravit.us/pro/content/homepage/series/series/overview/products~402880943a1b6e1b013a1bd20b39003d.us-en.html?product=592353&nser=0239&ncat=bidets The existing drain in the house goes straight down through the slab and the drain from this connects straight from the bowl down. The drawings are sketchy at best and it looks like this fixture may be able to be installed with a sink-like through-the-wall vanity connection albeit near the floor. No mention of a p-trap/s-trap in the fixture, like a toilet, and it is apparent that it does not have one by eyeballing it. Unfortunatly the guys that installed this fixture are probably not that familiar with bidet installation, and I fall into the same category with the one exception that I am trying to do it right even if it needs to be redone.