To navigate through Rock Tunnel
on Pokemon yellow on Pokemon yellow
You need a water Pokemon and the surf HM
To my knowledge i don't think there is a waterfall in Pokemon yellow and it is quite irrelevant to the storline if there was one. If you mean a HM named waterfall...i think your on the wrong game, only pearl and diamond have waterfall HM...i think. There are only 5 HM's in Pokemon Yellow Flash, Cut, Fly, Surf, Strength.
You cannot delete HMs in Yellow. It is said in the game that HM moves are permanent. If you will need to use HM's such as flash and cut that are not too useful in battles, just teach it to Pokemons that you will not use in battles so that your main roster's skills will be strong moves.
HM flash is located in Viridian City. Once there you must go into Diglett Tunnel and walk around for a bit. You will eventually come across one of Oak's assistants who will give you HM flash as long as you have 10 Pokémon.
HM 05 is flash
In Pokemon Platinum, Flash is a TM.
Look at "How do you get hm flash in blue?" On this site.
its not an HM anymore you have to find it.
You need to get and teach HM Flash to a Pokémon.
You can get the Hm flash of Pokemon silver is from the elder on the top of sprout tower in Violet city. There are alot of trainers through out sprout tower
you get the HM Flash after beating the electric gym leader, if i recall correctly