I found a Lavac Zenith at a Dutch boat jumble for 10 euros.
Replacement seals cost more!! The fresh water suction is plumbed into
a small 6l cistern which in turn is connected to the pressurised fresh
water system. Works a treat - flushing water drawn in, level in
cistern drops and float valve operates to fill cistern - just like at
home. Cistern does not leak when rolling - fitted in a motor vessel.