Don wrote:
I am installing a new head and am going to use fresh water for flushing
getting away from sal****er.

You aren't gonna connect a toilet designed to use sea water to your
fresh water system, are you? That can't be done without risk of
contaminating the potable water supply with e-coli, damage to the
toilet, or both...and every toilet mfr specifically warns against it.

ONLY toilets designed to use pressurized flush water can safely be
connected to the fresh water system.


I would like to know if the fresh water
will disolve the build-up inside the hose...

Nope...

... or do I need to replace the
whole sanitation line.

You don't have to do that either. A 12% solution of muriatic acid in
water will dissolve it. Or, if you'd rather not use muriatic acid,
repeated doses of white vinegar will do the trick.

It's about a 20 to 25 foot run to the holding
tank.

Unless it's all downhill, that's at least 4 x further than all but a few
high end electric toilets can move bowl contents...you'll always have
waste sitting in the line, and that will result in stinky hoses. The
optimal distance from the toilet to a tank is 6' or less...10' is the
absolute max.

So I think you may need a bit more help than you asked for. If you'd
like to email me, I'll be glad to help you spec out a system that won't
create more problems than it solves: phnlr (hyphen)misc(at) yahoo(dot)com.

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://shop.sailboatowners.com/books...ku=90&cat=1304