try putting a full 180 bend on the top of that, dust and dirt is not very heavy, and from looking at the top of your snorkle..i see an easy way for it to get sucked into the top of it. you may also want to check for leaks around the air box. the reason i said add another bend ( 180 total )..think of it like a drain pipe on the bottom of your house sink...it needs to be like the trap. just upside down..instead of water your dealing with air/dust/dirt. it really won't make much difference what you put on that..what ever floats in the air..will get sucked into it..but this will help cut down alot...in the mean time..i'll be thinking of a plan for putting some kind of filter at..or near the top.