Reverse a face or hide a face whilst using Sketchy Physics?

[test_user]

Hi
I am a complete newbie to sketchy physics and ruby....(have some experience with sketchup!....)

But, I have created a model with working levers and a bucket which lowers through a face (which looks like water and is ignored by sketchy physics) through to a face below which sketchy physics doesn't ignore! When the bucket touches this lower face the v small test script below works.
But i wish to make the top face of the bucket(group) look like its full of water when it raises again!
I have tried adding the water fill effect to the reverse of the top face and tinker with ruby code to face.reverse!
and also
I have tried adding a group(cover) over the top of the water face i.e hiding the water look face and attempt to then hide the (cover group) with ruby on raising to show the water face beneath.

But my lack of knowledge has given me a twitchy eye! hahahahaha
Can anyone show me the code?
Many thanks to anyone who can help me!

ontouch{|toucher,position,speed|
UI.beep
logLine("Touching Water")
}