So.. I was browsing various boards earlier and someone said they think the problem with ICs and their faint lines is the lack of dye, rather than lack of sensitivity. That was kind of the conclusion I had come to as well, from looking at so many pics of other people's positive, but faint tests. It reminded me of another post I'd seen somewhere online where someone 'hacked' them and I thought it was so genius, but I've never seen it mentioned anywhere before or since! So thought I'd share here:
Take 2 one step ICs, gently lift up the flap that is glued down on the pee end on both. There is a dye strip there, take that out of one and put into the other so you have 2x dye strips in one test. You have to keep hold of the bit that was previously glued down as this 'pushes' the dye onto the test surface, so yes you may get pee on your hand. Dip as usual and you should get stronger lines.
I haven't been lucky enough yet to get a bfp to try this on, but I tried it with my one step OPKs earlier this month (one I had already established it was a positive in the usual way) and it worked, two super dark lines!
I don't know if this would increase the likelihood of false positives though, so this comes with a HUGE DISCLAIMER to use this as a fun experiment (oh yes this definately counts as a fun hobby.. sort of) rather than a definitive indicator! I haven't tried it with a negative test yet, maybe I'll do that later this month.