I'm not aware of any lower drain for the bow thruster, so I'm guessing you're talking about the CDrive oil. Since you have access to the drain plug, I also assume you are on the hard. Are you doing routine maintenance, or do you have water in the oil? If it has been a couple of years you should change the prop shaft seals, too.
Drain the oil from the lower plug (it's best if you have something set up to keep the oil from draining all over the paint. If you do a search you should find a thread about this that describes a threaded pipe that goes into the drain hole.
After the oil has drained out, through the drain hole, suck out what oil is left in the bottom of the lower unit with a pump with small tube on the suction side of the pump. If your oil is milky, flush with some cheap oil a time or two (turning the p
rop several times) until it comes out clean. When you replace the plug, use a new oring.
For the Bow Thruster:
I assume the 54 bow thruster works the same as the SM, Paul. Remove the lower unit, turn it upside down to drain the oil. If it is milky, put a solvent in (like mineral spirits), turn the prop a few times, and pour it out, repeat until it is coming out clean. Either wait til the solvent dries (like over night), or I put some acetone in, slosh it around a little and pour it out. After an hour it should have evaporated. Then replace the oil, and reinstall the lower unit.
There is a good explanation of all of this in the files section. Read that before you proceed, and follow those instructions carefully. It's not rocket science, but eliminating steps, or ori
enting seals improperly will give you a less than optimal result. If someone sucked your oil out, they don't understand your boat.
Hope this will get you started. If I totally misread your question, try again.
Hi, I need to change my bow thruster oil. When this was last done they pumped the oil up from the bottom. Is this really necessary? Would it be possible to simply drain the oil, then fill from the top until the new oil starts to drain from the bottom before closing the outlet?
Amel 54 Ya Fohi