It is really good to see someone follow up with the results to their problems. Thank you.
As for the fill tube, There is only so much room under the bed for the tank and the tube. The tube is placed as high up on the wall as the bed will allow and since the tank's top is almost as high you get the almost level fill tube. The water fill device will help, trust me.
If you open both the cold and hot water drains and pump the water out, you will end up draining the water heater also. Please make sure the electric water heater switch (in front of the kitchen sink) is in the off position. If you run the electric water heater without water in the tank, you will burn out the heating element faster than you can read this post. In my case I only drain the water at the end of the season or if I think I got some bad water in the tank from a campground. I live in the country and we have a well with an electric water pump. When the electricity goes out we don't have water for toilets, showers or cooking, so we rely on the PC as our backup. Therefore I like to keep the fresh water tank, gas tank (for the generator) and LPG tank at or near full and the gray tank at or near empty. I always dump the black tank before coming home and put just about two toilet bowls full of water in the bottom of the tank to keep it clean.
Again thanks for reporting back.