I expect perhaps you need dampers on your input down there. Most
plumbers will sweat in a vertical pipe which provides a capped off air
column. Air will compress . . . water won't. At least not by much.

Mark 'Sporky' Stapleton
Watermark Design, LLC
http://www.h2omarkdesign.com

wrote:

Hi All,
I have a very weired problem in my basement bathroom:
Sometimes when I flush the toilet, it sounds like the system is
over-pressured -terrible, terrible sound is coming out of the pipe
connected to the toilet supply line, the supply line itself starts
going *crazy* moving from side to side. It stops doing so after 2-3
seconds.
I suspect some water pressure issues (I can't think about anything
else). I don't get how can this kind of problem exist in a single
pipe, while all other pipes in the house are connected. Is that
possible that over-pressure exists in a single end of the house water
system?
Is that possible that toilet tank can cause such an effect?
My biggest concern is that there is over-pressure in the system and it
might burst.

Thanks a lot for any advice.