Very true, that's why there are standard procedures for managing rebreather counterlung hygiene. In the case of hose pipes, they're quite difficult to dry out the inside as residual water collects in the bottom of the coils. A good blast through of compressed air (e.g. from a diving cylinder) goes a long way towards removing much of this water. But if planning to start a siphon by sucking on a hosepipe it's probably worth considering the use of a disinfectant first. Starting it by pouring water into the upstream end continuously via a funnel is safer and, in my experience, actually more effective.
