Following all the traumas of blocked tanks, manually pumping out from the deck fitting and trying to poke flexible cable up the skin fitting we finally decided enough was enough and fitted a macerator pump. This fits between the tank and the ball valve and is a Jabsco 18590-2092. What a transformation. In the last 2 years we have had only one problem when it would not pump out and this was easilly remedied by reversing teh polarity on the pump. We are still careful what we put down. We sue the dissolving toilet paper, which really works, and is cheaper from camping shops. We also use lots of water to flush. Also when pumping out, and you think the tank is empty, pump more water in which seems to dislodge solids stuck at the base. Be warned………………dont try and flush more water through the toilet whilst you are still pumping out as you will get your own back!!!