I don't know exactly; but you can chheck on Wikipedia. Just click on Adventure and click episodes. There you'll find names of the episodes and it'll give you a description of each episode. Look for the ones with Walmon in it.
in the undersea drive
Sirenmon evolves from Kiwimon, she is more related to bird and plant Digimon than the sea-based ones. Her full line is: Floramon > Kiwimon > Sirenmon > Ceresmon. Also, Whamon is more related to Digimon like Dolphmon.
Episode 21 of Digimon Adventure.
Episode 37 of Digimon Savers.
Her first chonological appearence is in the first Digimon movie. If you are referring to her first appearence in a proper Digimon season it happened in the 21st episode of Adventure.
Episode 33 of Digimon Tamers.
The next season after Digimon Tamers is called "Digimon Frontier".
The first episode of the Digimon Xros Wars, which is the next season.
Episode 51 of Digimon Adventure.
Episode 38 of Digimon Adventure.
Episode 15.
Digimon Adventure 02 Episode 38: A Very Digi-Christmas