First remove any extraneous optics from the optical path.

Second, be aware that there is only 1 (back focal) distance at which
all the aberations are optimized. This distance corresponds to the
normal attachments (diagonal,...). Go for a high power EP and a
moderately bright star--dim enough for you to see the diffraction
pattern with out glare from the central star, bright enough to see the
diffraction pattern clearly. For a 9.25" SCT this should be about M4.

Third, be aware that colimation at 10 waves is at best rought
collimation. After you get it roughly collimated, move inward to 3-5
waves and continue fine collimating. When this is optimized, then
proceede to critical collimation which is performed at the point where
the out-of-focus disk is collapsing into the focused airy pattern
(about 1-1.5 waves OOF). Here you are looking for symetry around the
not quite collapsed ring. You shold be able to get the not quite
collapsed ring to be symetrical on both sides of focus.

Use lots of magnification--at this point a barlow and your highest
power ep helps to see the diffraction pattern. I often use upwards of
130X/inch here. Say 3mm or 6mm and a 2X barlow. With a bright star,
you can use magnifications that are simply unreasonable for general
observations. You are trying to see the diffraction pattern of focus
not the image of the telescope. A subtle difference.

Ignore the spherochromatism inherent in these scopes while looking at
the symetry of the not quite collapsed ring. Look only at the intensity
and not the color pattern. It is common that one side will have some
flare like spikes around the perifery of the not quite collapsed ring.
Don't worry about these, worry only about the symetry of the ring and
get it similar on both sides of focus.

Then go for a cold one, you will have about expended all the mental
energy you can muster this night. And don't be worried if it takes
several nights of semi-frustration. Once you do get it perfect, the
scope will performe so much better you won't be able to believe it.
Then, once it is perfect, go very far out of your way never to subject
the scope to any jarring and it will hold collimation for decades!