Dave;

 

I have a similar setup; except I have the higher pressure cap on the first small filler bottle.  There can be residual pressure in the second tank because it takes some small pressure to force flow back through the cap on the first tank (at least on my Moroso cap).  I haven’t noticed any residual pressure in the first tank – except perhaps a bit of negative.

 

BTW; note that the total system pressure can go up to the total of both caps, in your case 33 psi.  This may be a bit stressful on hoses and the like.  I’m considering whether to just tighten the first cap, and leave the second cap on the first step of the latch.

 

Al