okay, so that was totally epic and near total disaster. I went with the pull the stand pipe method but next time i'm going to try my hand at the vacuum method lol. took 1.5 hours from start to finish. Luckily i pulled out 5 gallons and set it aside to lower the sump level which saved my tank from overflowing. twice i noticed at the last second that the tank was within 1/8" from completely overflowing the top, it was crazy!
Anyways, what happened was when i pulled the stand pipe, everything flushed down quick until it got to about 1/3 then stopped. All the dead snails and detritus over the last 3 years got sucked into the washing machine drain line and because of the ridges basically made a nearly complete plug in the line. I searched the sump and couldn't find the fish anywhere and checked in the overflow and it definitly wasn't there. so i figured i'd turn on the main return pump again to try and flush stuff through. wasn't paying attention and i was down in the sump when i was like "holy crap, why is my sump so low?" at which point it stood up and saw the waterline at the very top of the plastic rim of the tank and went for the apex shut off return pump button as fast as i could. Because my bulkhead doesn't sit right over my sump i couldn't risk pulling off the return line to the filter sock so i got some tubing and started trying to fish it down through the bulk head to clear the clog. luckily i thought, hmm.. if the fish is in there i'll probably crush him, so i went about going up from the bottom. I got it about 4" in the line and then WHOOSH, a flood of water shot out instead of the slight trickle and i manged to aim the water into the sump with only minor spillage inside the stand. so i pulled the filter socks, no fish and was like hmm... weird. So i tried turning on the return pump and i just couldn't get it to drain. so i'm no pro with duros stand pipes and thought maybe i messed it up somehow. after putting it in several times and adjusting the height nothing was happening (sometime around then i noticed i almost overflowed again, SUPER close call). At that point i figured there was probably another blockage but i couldn't get my tube in far enough to clear it because of the ridges on the drain line. Next i took a siphon and siphoned out all the water in the overflow (still was at like 40% high) because it wasn't draining. Next i unscrewed the drain pipe from the bulkhead and pulled it out. At this point I was 99% sure the fish was dead as it had been forever and there's no way he had water around him the whole time. The line had no water in it and i spent a minute or so with it over a bucked trying to straighten it out and look down the length of it to see the blockage when I spotted the fish sitting on top of the blockage not moving. So i straightened it real tight and shook it a bit and a bunch of shells and pieces of detritus fell out along with the fish.
Then to my surprise the fish started swimming around (i had done this over the 5 gallon bucket i pulled the extra water out with). Finally got everything back together and the stand pipe back in and tried to net the fish out of the bucket but wasn't having much luck. At which point it decided to carpet surf to freedom so i just grabbed it with my hand and threw it in the tank. Came out to eat tonight so all seems to be well now.
Man was that epic....lol
Thanks everyone for the help!