Okay, time to face facts- you're kind of a giant monster now. There's no getting around that. You still feel like yourself in your mind, which is a plus, but arguably less of a good thing are your multitude of "leg" tentacles spread across the grassy earth, your hard beak underneath large enough to swallow an average sized person digging into the ground, your long noodly arms ending in five smaller but still long tentacles, all dotted with suckers. Point is, you could be doing better.
One thing you've noticed is that you've stopped growing, presumably because mutagenic sludge is no longer being dumped on top of you. That's a good thing, but you are worried- that kind of toxic gunk could apparently turn a human being into an enormous cephalopod mutant, and all you did was drink a little bit of the stuff (and also take a swim in it like a chump, but hey, not everyone has good balance all the time, right?) For all you know, someone else might stumble across the same pond any minute now and make the same mistake you did, and who knows how another victim might handle being turned into a giant freak? You've taken the whole situation in stride, but someone else might not, and you wouldn't wish this sort of thing on someone that wasn't specifically asking for it (and even then, you might question their sanity).
So, it's time to take precautions. Reaching back down the cliff you just climbed- an easy task with how long your right arm tentacle has gotten- you stick you "hand" as far into the waste pipe as you can fit it, plugging it rather effectively (and rather benevolently, you feel). Almost instantly you feel the sludge begin to affect you body again; each of you tentacles stretch longer and grow thicker, packing on prehensile strength and power somewhat befitting of a giant monster. Your entire form grows taller, packing on feet in seconds as the cliff that less than an hour ago towered over you shrunk to little more than a step. Your arm is doing a great job of clogging the pipe, partly due to it growing longer because of the toxic exposure, which in turn has exposed it to more mutations than any other body part. You can feel each of your "fingers" snake out at incredible speed, shooting through the pipe through the building pressure of the mutagen. Suckers rapidly pop up on each branching tentacle, but because of the mutagen the quickly morph even further- each of the suckers starts to transform into tiny mouths (well, tiny for you, they're big enough to swallow a human being whole), suction cups opening up into actual porous holes on your "arm" and begin to slurp up even more of the gunk, effectively pumping the stuff right inside of you. It occurs to you that maybe this wasn't the best way to deal with the waste pipe, but your "arm" is already stuck pretty steadfastly in the pipe, so there's no backing out now, not until things resolve themselves.
Now that your body is literally consuming the mutagen, your transformation jumps into overdrive. Your huge black eyes shift to the side of your head as the skin breaks on you forehead, revealing another jet black eye quickly forming and growing to match the other two in size, giving you a conveniently much wider range of vision, while you head grows larger and more round, your brain inside growing to accommodate your new body's new functions. The whole experience is literally mind expanding, and you can't say it doesn't feel cool. What doesn't feel cool is the feeling of your mouth sealing shut, your lips merging together and your oral cavity filling in with whatever was inside your body now. It's not like you've been using the thing recently anyway, but still, you've spent most of your life with a mouth on your face, it's weird to suddenly not have one anymore. Where you human mouth used to be is now just another patch of slick purple skin, and just above that, your nose quietly closes off and shrinks away into nothing, leaving your face with nothing but three alien eyes to distinguish it. You wonder how in the world you're breathing, but assume you must be absorbing oxygen through the air or something like that; you sure don't feel like you're suffocating, at least.
Each of your tentacles has continued to swell and stretch, covering the green field you're resting on and drooping over the sides of the cliff; you must weigh several tons by this point and you're vaguely worried that the ground beneath you might crumble at some point from your huge bulk. Your hidden beak, growing sharper and harder and digging into the ground more and more, probably isn't helping. Your right "arm" is still changing more than the rest of your many appendages, growing wider and stronger, flexible muscle pumping up like a huge bicep, rippling with power. The pipe began to burst at the end where your "arm" was stuck in, the tentacle swelling with too much bulk to fit any longer. Sludge begins to leak out the cracks, and suddenly you're not so sure that plugging the pipe from this end was a great idea- you're very rapidly growing too huge to effectively do any damage from this end, and so far clogging the pipe has only seemed to turn you into even more of a freakish monster... Is this really still worth it?