There are a few options
one - you cold hold the hose a bit higher - so high the sand is not sucked into the hose, whil the debris is
second - you could use a smalle hose. The speed of the water equals the diameter to the third power (my brother, who is an engineer says), so using a 5 mm hose instead of a 10 mm will reduce the speed - and thus the power 2 to the power of 3 = 8 times
third - you could make a plastic bottle or so, increasing the diameter of the waterflow, while further downsteam the same small hose is used. The small hose dictates the water speed, and therefore, a 9 cm diameter bottle connected to a 1.5 cm hose results in a 9/1.5 = 6 times slower moving water - again resulting in suction of the debris while leaving the sand behind
fourth - a slow, lateral flow along the sand would move the debris while leaving the sand alone. A tiny pump might do the trick
fifth - your catfish will stirr up the debris, and it will fall down somewhere. If this is close to the pump - which should not suck form near the bottom, because of sand being bad for the pump - the debris will be sucked away. In the end, all debris will be sucked away
Option 5 is, by far my personal favourite - as is consists of doing nothing, just await what happens
I got 30 tanks with sand on the bottom, su I think option 5 does work