RO/RP1 realfuels crossfeed (new player)

[gonsy]

Hi there,

I tried to check on the internet about this subject, but i coudnt find a right answer for me, so i hope you can explain me:

Im trying RP1 for the fist time, so Im trying to build a sounding rocked, with the aerozine engine. Im using 1 on the second stage, and an other 10 more on the first stage.
Its quite getting there, using spin stabilisation and all that business.

BUT,  im getting fuel crossfeed for nitrogen. When I try to look it on realfuels, it says that that source it drains along the vessel.....WHY?

The only way that i can deal with that is using "ksp resource blocker" (I mean, clicking on the "menu" button to avoid the first stage to counsume the resources of the top tank). But it just gets anoying to remember to unlock it just before the staging time. Is there no other way to avoid bottom engines to take the fuel from the top tank? Do I have to install any mod? Is it there an option to avoid crossfeed, or am I doing something wrong?

Thanks