im trying to set up and undergravel filter system. but i think the bloke sold me something its not compatible with. and just generally im pretty clueless.
Well generally you place the undegravel part on the base of the tank, there should be a pipe in one corner... attach the pump into the pipe and this sucks water from the base part up the pipe and this pushes the water out into the aquarium...
sounds like he just sold you any old pump to go with it...
it shouldnt be loose otherwise the suction from the pump wont be as strong, you could take it back and show the guy or possibly use aquarium safe silicone to make it a tight fit