Non reversible for sure. Will have one large pump and manifold to fill each bag and each bag will have individual smaller pump to drain. Try to fill until that bag pukes over the side as stated before, or if you're no longer on the water, use your garden hose to fill the drain tube from the outside port on the hull. That will help prime the drain pump as well. If the drain pump is indeed working you are fighting an air lock which is very common with aerator style pumps.
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2008 OBV
325 EFI with closed cooling
Gravity III with 750's in the rear, 400 stock floor, 750 IBS
Servo valve ballast upgrade
Wetsounds Rev10
JL Amps, WS420BT
2000 Outback LS <-- Sold!!!
310 Carb Direct Drive
800# Rear Locker
750# IBS (should have kept this for the OBV)
Dual Batteries with 2 Bank Charger System
Kenwood Head with Remotes
Too many hours restoring exterior from prior negligence to count!