Inaccurate holding tank readings?

What puzzles me is there are no probes inside these tanks on the newer MH?The old excuse was [paper gets on them etc!!!!I don't think there is any contact between the sender and the internal of the tank.It is just a small unit on the outside of the tank?Maybe I don't uunderstand how these new rigs work but all indication is that nothing goes thru the wall of the tank?on't know hwat those Horst[sp] units are.Thanks for the replies If there is nothing into thru the tankwall not sure what the ice cubes will do to help but have heard of that for long time but never tried it.Old system could insert as tube into tank and spray usually helped for a while.!Still found the di[pstick most accurate if yuou could get at the top of the tank.worked for 15 years on my Eagle!