There are seven hoses to the valve. The four hoses to the loader are quick detaches so that's easy. None of the other three should drain or siphon the tank unless the tank line comes in low on the transmission. I'm pretty sure it doesn't. I think it goes into the top of the trans case. The tank line will be the other line that goes to the back that isn't PB. It crosses over to the left side and goes into the trans part way back. The PB line goes all the way back to the BH loop (or 3pt if you don't have a BH, and that's on the top very back of the trans). Of course there will be oil in those lines which will drain out.
Besides being ready with a container, I'd be prepared to cover the end of the lines to keep dirt out and stuff them up into the chassis until their end is higher than the level in the trans. Just in case.
You can contact your dealer and ask about this. If they're not up to it, you can ask the folks at Dave's Tractor in Red Bluff CA. Dave's also ships parts, in case you need cables....