The pressure of the water going up is not that much so it shouldn't dislodge the filter. When you originally fitted the filter did you fit the clip at the bottom of the chain to the bottom of the syphon tube and was it really secure? It's always worth making sure the filter is centred after putting the clip on. Also you shouldn't really need too much pressure when fitting the top to the bottom to form a seal in the first place. If you push it right in, it can be a bugger to get out at the end. Just experiment some more and use just as much pressure as you need to keep the seal.
Next time as you see the water starting to rise, turn the gas right down so that the water it still moving up but moving up very slowly. It's pretty much minimum heat on my burner but you may need to give it a little more. Also when you put the coffee into the top you don't want too much heat so that the water there is bubbling furiously. Another thing is when you are stirring, try and stir as shallow as you can and for as little time as needed.
My first few results were terrible but after I was shown how to use it properly, it's pretty much consistent now (in a good way!!).
By the way I'm not a syphon meister!! I've been shown the method though by someone who is.
Next time as you see the water starting to rise, turn the gas right down so that the water it still moving up but moving up very slowly. It's pretty much minimum heat on my burner but you may need to give it a little more. Also when you put the coffee into the top you don't want too much heat so that the water there is bubbling furiously. Another thing is when you are stirring, try and stir as shallow as you can and for as little time as needed.
My first few results were terrible but after I was shown how to use it properly, it's pretty much consistent now (in a good way!!).
By the way I'm not a syphon meister!! I've been shown the method though by someone who is.