Sounds like the pickup tube on the Dometic wasn't quite long enough for the tank depth
, 'cuz the tip of the "inverted bell" should just about touch the bottom of the tank.
If you replace it with a DIY
, cut the pickup tube at about a 25 degree angle. Any higher leaves too much in the tank, any flatter can trap undissolved solids and TP, blocking pumpout till they dissolve...which should only happen if the tank is pumped or dumped within an hour or less of the last flush, but can still be aggravating.