You could plumb a T in right before the pump with a cap or valve. A threaded T with a garden hose thread would be best. You don't have to put a T in, you can just unhook the feed from the pump every time if you want. Then you can hook a small hose up and drain into a bucket or use an external pump and pump overboard. I always bring my $10 drill pump attachment and cordless drill when I winterize. Comes in very handy.
Also your pump shouldn't have a problem pumping the whole tank. Check your water pressure, maybe the pressure switch is faulty and the pump is trying too hard. You shouldn't need more than 30-40lbs or so.
_________________ --2002 3880 Regal Flybridge | Twin Merc 8.1HO **Seven** --2003 AB 13 VST Console Inflatable | Tohatsu 40hp TLDI **Phish'n ski** --310 Mercury Inflatable | 1982 9.9 Johnson
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