I've got a fuckin beuty of a suggestion(we used to do hot knifes as well) maybe you already know about this one.
Its called "The plunger"
Here's what ya do. Get a 2 or 3 litre plastic botttle an cut of the very bottom of it, fill a bath, put the bottle in the bath so the top is sticking out of the water, wrap tin foil round the top of the bottle, pierce holes in it, put you hash on the tin foil, about 2 or 3 joints worth, get a real good lighter an start burning the hash, as your burning very very slowly start lifting the bottle, by the time you get to the bottom of the bottle(obviously the bottom is still in the water or you will loose all the smoke) all the hash will basically gone, an the 2 or 3 joints worth of smoke will be in the botttle, take of the tin foil, put your mouth round the bottle and push down on the bottle an take one big breath,an try not to choke, keep it in as long as possible.
There you have it "The Plunger" 2 or 3 joints in one puff!
You really have to do it the way i said, cuz you will fuck it up if ya dont! the bottle has to stay under the water at all times, you cant put the hash on the bottle before hand cuz it will get blown of when your pushing the bottle in the water.