A pretty decent filler, but that is what is was, filler. To answer a few questions above (since I have nothing else to say here):

* They didn't put Wailmer into a Pokeball because I don't think Luxio would have allowed them (or at least fight them not to) and if Ash did Wailmer would have been transported to Professor Oak. They might as well just help the Wailmer out of the sewer when it's right there.
* As for catching Swampert, I don't know. Probably because it wouldn't be right to take it from its territory (though it acted like a jerk about it, Ash and co. and the other Pokemon did trespass). Usually all of the Pokemon Ash and co. catch want to go with them willingly before they are captured. Also, Ash has Buizel, he doesn't need another Water-type.

Now, onto the review:

A Pod And Group:
* The boats aren't running? So I guess they're spending another day in Canalave... whoa, a pod of Wailords!
* No one knows why the Wailords are in the harbor? Maybe Ash and co. should send Buizel and/or Piplup to ask.
* Then again, once Ash's stomach rumbles he's pretty much useless for thinking until he's fed. *sigh*
* Err... guys... better be careful... you have a pair of glaring eyes watching you ea... change that to stealing the Pokemon food.
* Ash, unless you're referring to the one in the movie, you haven't seen a Luxio. But oddly enough, you did see its Base Stage (Shinx) and 2nd Stage (Luxray).
* Bad move Piplup, Luxio is an Electric-type, and though Pikachu isn't the greatest match it can hold its own... a Whismur?
* And Ash got tackled by a Nidoran (male), are those three Pokemon working together? Oh, yay, they were. And of course Piplup doesn't know when to leave things lying down.

Trapped Down Under:
* Here's Team Rocket working to earn some cash like usual. Oh! the three Pokemon just ran past meaning Ash and co. aren't far behind.
* Wait a second, they already have a mecha ready? So are they working because they spent all their money on building it or did they work here then spent their money customizing mecha-fying the excavator?
* Team Rocket wasted no time attacking Ash and co., they in the process they did blast the manhole cover open for Ash to get into... and then crushed it.
* Looks like Ash and Pikachu will be following those three Pokemon (you know, cause it's not like a Pokemon could blast the manhole cover off).
* Canal? Ash, it's a sewer, of course it runs under the entire town! At least Buizel will be able to navigate without trouble.
* Oh, those three Pokemon and the Luxio doesn't like Ash and Pikachu being down here. But Ash, why use Buizle against Luxio, you're lucky it only did a Iron Tail.
* Once again that Nidoran (male) caused the distraction (this time Pin Missle) and allowed them to get away. Though they couldn't have gone far being there is only two directions.

No Feraligatr In This Sewer:
* Ah, so those three Pokemon stole the food to feed a Wailmer... hmm, maybe this Wailmer is part of the pod of Wailord blocking the harbor?
* Careful Ash, that Luxio still is kind of mad with you, though it seemed to have accepted your help in pushing the Wailmer. I'm gonna guess it got stranded in the sewers and the pod of Wailords are looking for it.
* Whoa! Okay, them spraying water on it didn't give them the effect they wanted but did get the Wailmer back into the water (and pretty happily).
* Meanwhile as Ash, Pikachu, and Buizel tag along to help the Wailmer get back to its pod, Happiny is taking its shot at pulling the mancover off... but couldn't.
* NO DAWN! NOT MAMOSWINE!... Oh, it's just ignoring her. Phew... OH NO, NOT POFFIN!... Oh, it got the mancover opened... and sent Dawn flying into the air (thank goodness Happiney was there to catch her).
* Whoa, a habitat of sewer Pokemon. They have a nice looking place (they even have furniture and a TV!). Surprise there are now Totodile (or any of its evolutions).
* Dawn and Brock are finally in the sewers, and Piplup is leading them to who knows where (probably right into a Feraligatr).

But That Doesn't Mean There Isn't Another Fierce Starter:
* Oh, so that's why it couldn't get back up, there's a little waterfall Wailmer fell down from. A peice of rope and everyone pulling (and Buizel puhing) fixed that problem though...
* OMG... I don't think a peice or rope and pushing a and pulling is going to go over this waterfall (what kind of sewer is this anyway?).
* Of course, just when Ash and everyone left, Brock and Dawn come out from a door near the top of the waterfall. So I guess Piplup was sorta leading them in the right direction afterall.
* Whoa Ash, that's kind of a far fetched plan if you ask me... but it looks like it's working so far... Gah! The ramp broke! Oh, lol, I guessed since Venonat wanted to do something since it didn't help in the construction and helped Wailmer get a little bit more air to get to the top.
* And as they are walking to the exit they all meet up with Piplup, Dawn, and Brock! Guess Piplup did come through afterall. Whoa Luxio, becareful where you do that electric shock if you know what I mean!
* What's that moaning? Ah oh, I knew it was coming, there was no way they couldn't have put this reference in, here is the... Marshstomp?... WHAT ABOUT FERALIGATR!!!
* Brock, don't question Pikachu's electrical attack abilities! It had hurt plenty of Ground-type Pokemon with electrical attacks! It would have made more sense for you to say the attack could hit Wailmer.
* However, Grotle is a better choice as Marshtomp is quadruple weak to Grass-type attacks and Grotle is immune to Water- and Ground-type moves. Wow, Marshstomp was a pushover...

Evolving A Few Seconds Too Early:
* They are finally out of the sewers and now Wailmer... I mean Wailord can rejion its pod and leave the harbor (good thing it didn't evolve in the sewers!).
* Oh come on! Wailmer, you couldn't have evolved AFTER you crossed under the bridge? You better hope that is a draw bridge or you're going to have to do a Free Willy jump.
* Notice how only Pikachu eletric attacks are yellow while Luxio and Pachirisu's are blue and white. Though I don't know what Ash plans to get against the Swampert by diving into the water (couldn't they just have Wailord lift its tail to launch Swampert like Team Rocket?).
* How odd, the Rattata and Nidoran must know an Eletric-type attack (They can learn them via TMs in the game), but if it gets the bridge to go up faster then okay!
* See? Ash didn't need to dive in, just from moving ahead Wailord caused a giant wave whiched pushed Swampert back (though somehow missed Ash who was right next to Wailord).
* And with this done, Wailord and its pod leave and Ash and co. can leave Canalave finally... after they eat, of course. -_-;

i have a whole list of ranting but tv dot com didnt let me post it so ill just post this main rant:

swampert isnt strong enough to take on wailord it mustve had a ginormous ego

how is it that wailmer cant be pushed into the water but it can be pulled up a waterfall