It is well accepted that to run most of the time with a low quantity of fuel in your tank will lead to ccondensation, this is mainly due to the fact that even after only a relitively short run the fuel will warm up in the tank forcing air out, when the fuel cools overnight it draws in new air which will have moisture in it, with a nearly full tank this effect is much less pronounced, due to the much larger volume of fuel not getting as warm and the much smaller air space, so morral of the story keep your tank topped up very especialy after a long run, try not to park it up with nearly empty tank, the fuel will not just be warm it will be very hot, pull into a station and fill up before leaving it, Rick