I had to rebuild the hand pump in my '78 Trillium
However, the hand pump still required many strokes
to get water from the tank to the sink because
hand pump was not air tight and let the water in
the line flow back to tank. The problem was solved
by installing a check valve about a foot below the
pump. Now water is right there... one stroke of the
pump handle starts water flowing from the pump spigot.
Here is a source for the check valve:
1/4" PP Standard Check Valves | U.S. Plastic Corp.