Wouldn't the easiest solution be to just purchase a fitting designed to accept the drain line from a dishwasher and use that? Not sure I understand the question...that picture doesn't help...
I have drain lines from all my basement tanks connected to a manifold, each intake on the manifold has its own valve, and these valves are used to determine which tank or system the central pump is drawing water from during a water change. On the outflow side of the pump, a Y-fitting, again with a valve on each arm, controls where the water is sent. One side, used in the summer, pumps the water in to the drain line from my basement floor-sump, through the foundation wall and into a Big-O drain line that runs into an adjacent field. Simple and foolproof. In your case, with constantly running drips, I think it would make more sense to have the overflow from all your tanks run to a centrally located basin, from which a single pump operated by a float switch ejects the water.
In my case, the other side of the Y feeds a wall-mounted exterior faucet. During winter...I know you don't have this issue...a hose is laid out before each water change to carry the water to that fallow field, and the hose must be rolled up immediately after the change is complete, before it freezes. But in the summer, I leave the hose attached all season, which lets me use the ejected tank water on my plants, flowers, garden, etc. You might find that to be a feature that you could use all year round.
