potable water tank

Does anyone know if the fresh water tank can be opened from  inside the trail manor-there is something that looks like a plug on the top but it seems to be sealed

[Sinclue]

I replaced a water tank on a previous trailer and it had extra "holes".  I was told it was so that the tank could be installed in different ways (basically vertically or horizontally) depending on your application.  All the holes were sealed when I got it and I had to cut out the ones I needed to use.  As I recall I had two "extra" holes I didn't need to use.  If you did take the plug out you'd want to make sure whatever you were going to do would keep the hole sealed up during travel if you carry water in your tanks.  Wouldn't want water sloshing out of the tank.  
Jim

[Bill]

This may be obvious, but the entire tank is lower than the fill port on the outside of the trailer, and lower than the vent port which is part of the fill port.  Therefore, if you cut a hole in the tank, even in the top of the tank, the hole will also be lower than the fill port.  As a result, you'll want to seal up whatever you attach to the new hole REAL GOOD, or it will seep while filling as the tank gets full.

You didn't mention what your application is, but if I felt I needed an inside port, I think I would put a tee in the fill line, well clamped, and run it to a garden-hose fitting inside.  Then use a garden-hose cap to cap it off.

Just a thought ...

Bill