Verified answer

Don't teach HM moves to your main Pokemon, use dedicated HM mules for that. Only Surf and Waterfall are HMs that are worthy of a spot on your team. Use the following for the rest of the HMs (assuming your Empoleon knows Surf):

BIBAREL

Rock Smash

Rock Climb

Strength

Waterfall

DRIFBLIM (Drifloon can be found on fridays @ Valley Windworks)

Fly

Defog

Cut

Flash

or you could use

TROPIUS (Great Marsh)

Fly

Defog

Cut

Flash

GOLDUCK

Rock Smash

Rock Climb

Strength

Waterfall

These are just suggestions, these Pokemon can learn more HMs and other outside-battle-effect moves than the ones suggested, just puzzle for a bit until you find the HM mules you want. These aren't intended to be used for battle, just for utility. http://www.serebii.net/games/moveset.shtml

if you really don't want the gravler try to find another rock type to replace him with not try to tell you what to do but personally drill peck is a little better than rock climb i made the mistake of letting my empoleon learn rock smash and later realized that it was a bad idea now i got a new team

I suggest you to catch a new rock pokemon , onix is a good one but it depends upon your choice.when you have caught the required pokemon you can get rid of graveller