I use one of these.
It is from motion pro. You can rig something up with a tube and a turkey baster if you need too.
The slide is adjusted to the fork oil height (distance from the top of the fork tube) you need. Fill the fluid up to a level above what you need, suck out what you don't.
This is done with the fork full compressed and spring removed if there is one.
You are going to level, not quantity.
Right leg gets 38mm (approx 405 CC)
Left leg gets 87mm (approx 410 CC)
Left leg is measured without spring. Pump leg 8-10 times then measure.
All levels measured with leg compressed.
Shout if you need anything else.
The best thing to do is match the viscosity, not the weight. The "weight" can vary drastically with manufactures. Find your oil on this chart, then find something close you can get.
http://www.peterverdonedesigns.com/lowspeed.htm
Showa SS-5 is 15.68 cSt @ 40C find something on the chart you can get that is close.
Yup, oil height. After the valving is covered with sufficient amount of oil, the important part is how much air you have above the oil, not how much oil.
Volume is just to give you an idea....
Was it this one? http://www.trialscentral.com/forums/topic/32873-suspension-set-up-jxt270/page__p__249919__hl__%2Bstatic+%2Bsag__fromsearch__1#entry249919
Unloaded is the bike on a stand, no load on suspension. Loaded is you and gear.