Now, when I drain them, the wet tank has next to nothing and the others nothing at all.
The goop will not neccesarily come out if you give the drains a quick blast. The air pressure races out the drain, over the top of the sludge and prevents it from moving. The sludge will drip out slowly after the air is gone.Picture the dirt in the bottom of the bathtub. It leaves at the end, when there is some flow at the bottom.Cable drains are great for ease of a quick drain, but a real contributor to problems, since they cannot be easily left open overnight, and often have fairly small openings.Want to see how yours is?Drain all the air, and leave the drains open. Remove them, if it is easier than tying the cable back. Opens a bigger hole anyway. Position a piece of paper towel under each drain and see what you get overnight.Hopefully nothing but a drip or two from the wet tank.