Most contest pilots trim their sailplanes to the most
rearward permissible position.

I have found that many sailplanes don't like the full aft CG position. My
ASH-25 handles best at about 75% of the allowable range and the LS-6 is about
80%, I'm told the Discus likes to be about 92%.
If you go too far aft with the CG, you will find yourself trimming forward,
when you drop the flaps and enter a thermal.
I use the tail tank to find my best CG position, dump a little until she feels
right and then after flight, dump the tail water into a bucket and weigh it.
That is the weight that I add (in lead) to my tail. Then when I fly with water
in the wings, the tail water only balances the added weight of the water in the
wings.
I restrict the tail dump line, so that it will dump proportionally (at the same
rate as the wings) and this allows me to dump a part of my water and still
maintain my ideal CG position.


JJ Sinclair