I have 2-70 gallon tank in the boat. you fill the first tank and then it gravity feeds into the secondary tank. the problem seems to be the connection between the two seem to be greatly restricted. I can't get to the fitting without removing half of the interior. Does anyone know about what might be used to clean the tank scale. The water seem clear and clean but I would imagine after 30 years (and no filter)the scale has probably built up around the exit form one to the entrance of 2. They are aluminum tanks. I plan on putting filters in when this is done.