Greetings,

The most common things that will cause a piston type pump to lose it's
ability to draw a suction is an air leak in the supply line.  Sometimes even
a pinhole will do it.  Of course, you could also have a bad seal or valve
leaking air as well.  Either way it may be very hard to track down the
cause.

If the valve position for city water does not work, you either have a bad
selector valve or a clogged line.

I have a 1998 Coleman Sea Pine with what I believe was the same 2 way faucet
you have (if you have the one installed from the factory).  I got tired of
the inconvenience of it and took it out, cut a rectangular piece of aluminum
plate to cover the hole, drilled holes for a standard size laundry faucet
($15.00 at Home Depot), and just directly connected the lines from the city
water connection to it.  I sealed all the edges with clear silicon caulk.

I then removed the built-in water tank, and when we need to carry our own
water we just buy a few 2-1/2 or 5 gallon jugs of water at the grocery store
(the kind with the pull-out spigots) and use those instead.  It would have
been easy enough to install a small 12v electric water pump to move water
from the tank to the "hot" side of the new faucet, but frankly I didn't want
to spend the time and money.

Having a single purpose all-metal faucet for use with city water is much
more convenient than the orignal plastic one.  Just the higher arch makes
filling pans and washing dishes so much easier.  I'll never go back to the
old plastic faucet again.

Cheers - Jonathan

Had the same problem with my Starcraft Galaxy faucet. I got this kit and
rebuilt the faucet and it works fine now. However, it took several hours and
a steady hand to replace the seals and clips. A local dealer had it in
stock. It was $20 + tax.

http://www.go-rv.com/coast/do/catalog/page?dealerId=557&pageNum=387

Item #  25096
Repair Kit # 199-9