Replacing toilet on Ericson 38

[Byrdhousemedia]

I put in a new CW (Junior)toilet in the head. I bought it second hand, although it had never been used. I got it because I wanted more flushing power. I took out the old one, seated the new one, and hooked all the hoses up. Trial flush....it doesn''t suck water through the intake.
Seacock is open, the vent on the loop is open, and it does siphon okay. No problem flushing, but no sucking.
I tightened everything down to rule out air leaks, but still no go. any ideas what to look for?
Michael Byrd of the Lucky Jack
Seattle
moored in fresh water.