Fuel pumps are good at pushing but lousy at pulling so keep the feed line as short as possible and big bore (remember big bore is not the same as big o/d).

Rigid UAT's do not function any better than flexible, what matters is the pressure drop on the feed side and pressure drop is caused by restriction. Chances are if a rigid UAT has cured a flexible UAT problem it is because there is less restriction.

The flexible UAT's I use on Merlin/Rhino 170's do depress slightly at full power but still maintain good fuel feed without cavitation.

Hope that helps.

Rob.