Hold up on adding SAE 30 engine oil unless you are confident that's what that tranny requires!! Some units require automatic transmission fluid. You need to verify the proper fluid from a Yanmar manual or other reference.
Here's a link to a Yanmar Help. It turns out that SAE 30 is the proper oil for your model tranny. http://www.yanmarhelp.com/i_box2.htm
I think it would be impossible to rid the transmission of all fluid using a suction pump....best to go with the dipstick measurement.drchpete said:After pumping out and refilling the transmission oil with 1.3 L as required, the dipstick read overfilled. I had to pump off another pint or so to get it back down. Does this simply mean I didn't get all of he old oil out? It sure made that sucking sound from the suction tube. Do I believe the dipstick or the amount called for. I did not screw the dipstick in when checking.