Can Blastoise learn Water Spout and Yawn in HG/SS?

Question

Trying to get my Blastoise in SoulSilver to learn WaterSpout along with Yawn, but to do so would mean that the male parent needs to know both moves. Is this even possible?

Answer 1

In games prior to Gen 5 (BW/BW2), only the male can pass down Egg Moves to the offspring. Heart Gold/Soul Silver are gen 4 games, and as such the move combination is not possible, as there is no compatible breeding partner for a Blastoise that can learn both Water Spout and Yawn together. The only compatible partner for Water Spout is Octillery, which cannot learn Yawn.

In Gen 5 or newer games you won't have this problem, because the female can also pass down egg moves. This would allow you to breed twice and get both moves on the same Pokemon -- first breed in Water Spout from a male Octillery, then use the Squirtle offspring with Water Spout to breed with any compatible Pokemon that can learn Yawn (the page for Blastoise' Egg Moves shows 6 evo chains by level up, and another 5 via breeding).

TL;DR -- The combination of Water Spout and Yawn is not valid in games prior to Gen 5

Answer 2

Unfortunately, it is impossible to get both Yawn and Water Spout in Gen 4. Like you said, the male would need both moves, and no compatible parent can learn both Water Spout and Yawn.

source: https://pokemondb.net/pokedex/blastoise/egg and I also done the test in the Pokémon Showdown! team Builder