Did your fantail have a swim bladder problem BEFORE he got stuck in the filter or is he not able to swim upright because he got stuck in the filter?
If you have aquarium salt I would add 1 tsp per gallon of water.  That will help with gill function and electrolytes.
Have you heard of Melafix?  It's a great tonic that will help heal his torn fins, scrapes and bruises.

What kind of filter was this? 
Keeping him in shallow water will be good until he gets his mobility/equilibrium back but you may want to add a slow aerator. You can buy very cheaply, an air adjustment valve so you can just have a slow steady stream of bubbles rise to the surface so he gets the dissolved oxygen he needs while in the smaller container. Also, you will want to change at least 50% of the water daily while he is in the travel container.
Please keep us updated on his progress and we wish you all the best!

Unfortunately Bubbles died this morning.
I bought lots of stuff for him and was very careful not to overdose him.
He did eat a tiny bit yesterday, I hand fed him, but last night when I tried him with a bit more he spat/vomited it back up. He seemed really out of it after that and he took his last shallow breaths in front of me early this morning.

Thank-you very much for your help, I guess he was to badly injured internally to save.
We had his funeral this morning, my daughter made a paper box with a woven lid for him (actually we found out he was a she) and she put rose petals in with him. We all said something and his body is now with the earth.

P.S. I'm cross with the vet he didn't phone until 8.05pm when I was away to the pet shop, when I got back and phoned him, I got an answering machine. It angers me that people don't take a goldfishes life seriously. Waiting all day for nothing. I'm glad I found this site, it's very informative.

Our filter has got slots too, but how small was Bubbles that he could get sucked into it. Suppose he was tiny?
It is always sad to hear a fishy pass away into the big tank beyond... 
 It is true, 35 l is too small, we learned this lesson too, and we were told the same, no, worse: when we first got our 2 fishies we were told the 5 l tank is sufficient. ... OUGH.. we learned very quick ... so we bought the Aqua One 380 which is a 34 l tank. It was OK for another 4 months, now it is too small and we're looking forward to move our 2 fish into the 150 l tank we set up last week.

So it is very wise to get a bigger tank and appropriate filtration. A good filtration should turn at least 3 times the tank volume in an hour.
Maybe you do have time to read some posts in "Tank and Equipment" sure some helpful things in there too.

All the Best

Hanna

Hi, yes I think he must have been weakened in some way already. He looked fine and playful the day before though. I bought a fish disease book shortly after getting him as he had fin rot. We got him in a pet shop that don't really look after their fish, but we made him better and we had him for about a year and a half. The day before he got trapped we found him hidden behind the filter but he swam away fine when I lifted the filter away from him. It's very strange, he was small but I still think he was too big to get sucked up the filter! And yet there he was, I saw it with my own eyes.

I will be testing the water as we still have our other fish Lily in the tank, we've had her for 2 years, she looks healthy so far, I've been even getting up at night to check on her, I'm sooo worried, she's twice the size that bubbles was so hopefully she will be ok.
The only worry with Lily at the min is that she keeps hovering around the bottom of the filter! I have watched her alot and can see her swimming fine, she swam up to get her food and down to rummage in the gravel and through her bridge, so she seems ok. There is no sign of anything on her, I really hope she stays healthy.

I had never heard of testing the water until reading it on this site but will be doing it now.

I have read lots on this site and I will be letting the tank sit set-up for two weeks, or shorter, if Lily needs in sooner. We did actually do that before getting Lilly, we had the tank set up for about 5 days, my son had read it somewhere.

We picked our new 110 litre tank yesterday and we are collecting it today. We found out about a specialist fish shop near us, though so well hidden we never new it existed until told about it. It is fantastic and the fish look sooo happy and healthy. The owner is v knowledgable and well respected by his customers. One customer told the owner that every fish he has bought from him is still alive.

We're excited about making Lilys life better but disappointed that Bubbles won't get that chance. We'll buy a new friend for Lily from the fish shop in a couple of weeks time.

I will definitely be asking more questions!

Poor Bubbles.   I think you tried your best.  Sometimes accidents just happen.

Im so sorry to hear about that. I hope lily finds a new friend to get along with!