OK, Kirby...it's now time to decide just how serious you want to be about pumping the bilge
. (Note the sign-off from Kai-Nui; do you really want to be that scared...? <g>)
Yes, you should install a 2nd, dedicated discharge line, as direct, short & nonconvoluted a hose run as you can. The reason is of course the rationale for the 2nd hicap pump in the first place: you suddenly discover your standard bilge pump
is not staying ahead of flooding, whatever its source. At that instant, you want the hicap pump to actually BE a hicap pump. Moreover, you probably do not want to give up the manual pump's effectiveness by filling its discharge line. Also, each check valve you might add to an existing discharge line provides increased flow restriction. Take a good look at a 1.5" check valve and thing about the flow of a liquid. Again, ask yourself why you are adding the hicap pump.
I think you will find the hicap pump has a 2" discharge, so your first issue will be whether to reduce that to a smaller diameter. Adding an anti-siphon high up for a 2nd, dedicated hicap discharge line will add flow restriction, too - it isn't a perfect world and I don't mean to be painting a black vs. white choice. But you have a very nice boat that's capable of some serious cruising, so think about her future and not just the period you own her. We sail short-handed (husband & wife) offshore
, and for me there's no real choice here: do I want it to LOOK like I have max pumping capacity for the pumps installed, or do I truly want it. Be honest with yourself, think about your crew and your plans, and perhaps running that dedicated discharge line won't seem like such a big deal.