I have a female Charizard and a male Tyranitar that knows Rock Slide, I have tried to breed them several times. Each time they produce a Charmander egg, but without rock slide. Please help
Based on the information you've given us, this SHOULD be working. Double check that your Tyranitar hasn't forgotten the move at some stage. The only other possibility is a fault of one sort or another (for example, if you're playing a PC rom, it may be corrupt).
First off, what generation/game are you trying to do this in?
Secondly, as far as I know only generation 4 and below let you transfer Rock Slide as an egg move.
Anything that is gen 5 or above doesn't let you transfer Rock Slide down.
Check the Charmander Pokedex page and scroll down to the moves part, there is a section labeled Egg Moves, all the moves in that section are the moves that you can transfer down to a Pokemon through breeding.
Hope this helps.
because it's not a egg move for charizard or charmander, he can learn it through tm.