Essentially, you are asking, "If I couple my new solar water heater, to a secondary smaller, home-made, solar water heater, will I get more heating?"

This is a question I can answer with an absolutely definitive, "Maybe!"

If you
+ using enough tubing, and
+ don't screw up the flow by introducing too much pressure loss, and
+ connect everything properly,
then, you'll get a little more heat . . . if the sun is shining brightly.