I Use ATF(Mobil Dextron III). I drain the fluid and then put the drain plug back on after draining. I then pour some ATF into the bike through the fill hole. I use paper rolled up into a cone as a funnel. Now I take the plug out again to let the fluid out. This flushes it out. Next, I wrap some teflon tape on the drain plug screw and put it on. Be sure to put it on in the right direction. This will prevent the bike from dripping ATF on the ground(Happened when I bought my tomos). I take the overflow bolt out and put some teflon tape on it and leave it off. I fill the bike up with ATF untill it overflows out the hole and then put the bolt back in the overflow hole. I put the bolt on the fill hole and I'm done. Its that simple! I have a '98 Tomos Targa LX if you were curious what I had.
I always change the trans fluid 500 miles or every 3 months.
Swarm and Destroy!