I was going to change the lower unit fluid, but I can't find a drainplug. I read on another thread that it could be behind the prop? If this is the case, what position should unit be in during draining and filling? Thanks!

behind the prop, drive down.
Make sure you don't loose the plug seal. It sticks to the drive many times.

Thanks...should the drive also be down when filling? My manual says the drive should be up when draining and filling, but it also says there should be a drain plug on the side.

you want it tucked all the way down, even if it means putting a floor jack under the back of the trailer to get the clearance to run it that far down. Even with the side mounted drain this is the way to do it, never up, you won't get all the oil out and you will end up with alot of air pockets in the drive.

You know to fill it from the bottom, right???????

haha..yeah, I do know that much...it just threw me off when I didn't see the plug at the bottom...I pulled out the manual, and i said it should be there...it also said to fully raise the lower unit before draining and filling. I can see how if the plug was on the side toward the back, it would make sense to have it raised for draining, and I can also see how if the plug is behind the prop you'd most definately have to lower the unit to get all the fluid out...I just didn't know which position it should be in during filling to get the proper fluid level.

After you fill from the bottom and you are ready to remove the pump run the drive all the way up. It helps slow the gear lube from leaking out when you replace the plug.

If your drain plug was on the nose and you wanted to check for water you would trim the drive to the up position and drain some into a glass container.If it was behind the prop it would be in the down position to check for water.After it was done draining you could bring the drive up just to clear all gear lube that might be on any internal driveshaft housing ledges.