Well got info on these extended tanks supposed to let you run 12 or 15 hours b4 refill on tanks. cost is $129.99 and seems high[I can't find correct fittings to make my own] but comes with all correct fittings and instructions; you must remove the vents in the cap[s] of your honda[s] and run lines into them...ships fast too.
heres the link and you can look thru, has setups for other gens too.
http://durationpower.com/store//page4.html