FIRST-- use the same gage for BOTH tanks, just use a gage selector flip switch like the m52s, 51s, 62s, 543s
SECOND--- use a transfer pump (same pump as the 109 box heater ) from the second tank to the draw dank, like the m51a2s, m52a2s, m543a2s, if up dated m62a2s , again a on/off flip switch...