iv run my cooltube setup for several years and have experimented with the configuration quite alot, ive found it makes no difference sucking or blowing air thru the tube, on paper its better to suck air away from lamp, but iv found this makes no difference, for the ideal cooltube setup you need two exhaust fans, one (just to cool the lamp) to suck or blow air thru the tube from either outside or another room thru the cooltube and straight out into another room then another fan to exhaust yr growroom air and keep fresh air entering, this setup is ideal if u are running Co2 enrichment coz u can slow or shut down the growroom exhaust periodically while yr Co2 is doin its thing, and the other fan is still cooling yr tube preventing heat build up. I have my 5" exhaust fan mounted directly to the c/filter then a short length of ducting down to my cooltube with a 600w hps then a short length of insulated ducting (to prevent the hot ducting heating up my room) out to another room, so my one fan is doing 2jobs, cooling my lamp and exhausting filtered air from my room, people have told me this wouldnt work, but the proof is in the pudding, my temps average 26degrees c, even on hotter days, with shitloads of fresh air stil being drawn i from the passive intakes in my tent! i dont like the idea of sucking air thru my fan directly from the cooltube as the air coming out the cooltube is quite hot and im pretty sure it would shorten the life of my fan?? but in short imho suck or blow, it makes no difference