Tranny Fluid
Hi John, sorry to hijack Don's reply. The end bell is the tranny case. Normally the aft side of the case has a stamp or label that will tell you what you need to know. Make, model, etc. As Don said, I would vacuum the fluid out with a pump, much the same way you extract oil from the engine.
Transmission differ on lubricants. Check your owners manual, or contact Yanmar once you have the model information from the end bell or case. Our 2GM took regular engine oil. Our current boat takes ATF. If yours is leaking red oil, then it could be ATF. Why/where is it leaking? Do you need to fix that leak first?
Also, most transmissions take very little fluid. The very end of the dip stick has a mark. That is the full mark when the dip stick is resting on the case, not screwed in. Maybe a pint of fluid...maybe.
As a foot note, the 3GM normally used a Kanzaki KM3P transmission. The end bell will tell you.