Leave the antisink in peace, its only job is to keep the car up when
it's not running.

When you start your car, do you mean 'starting the engine' or 'setting
the car in motion'?

If it's starting the engine, do you have the foot on the brake? Do you
press it down hard? The rear brake gets fed from the rear spheres, which
helps to keep the car level under hard braking. You may want to try not
pushing the brake while starting the engine.

If it's setting the car in motion, that's the way they're built, the
rear trailing arms in combination with the very soft suspension makes
them go down. Enthusiasts call it 'dropping on its knees in honor of
Mages (the designer of the system)'.

In general, as long as it's soft, don't touch anything. These things
have some life of their own, and that's ok.

cu
 .\\arc

When you start or when you stop? If it's when you start then it's probably
not the antisink valve.

Late Xant/XM, or C5?

Sounds like your accumulator's flat, so when the pressure rises to the
point where the antisink gets turned off, there's insufficient reserve to
hold the car up. Antisink sphere may be flat, too.

When were spheres and fluid last changed?

when i bought it the back end drops when i start the engine so when i got
home i took all my spheres off my other citroen xantia witch inew where ok
is this any help thanks