I would say it is the suction for your LW if it is below water level. You should also have an overflow for the LW, and sometimes they are below water level and some are above. I am not familiar with the Fisher boat but I am sure its like most boats LW systems. You should not have to plug the LW ever. Do you have a 3 way switch that says AUTO, OPEN, REC...If so just leave the 3 way switch in the open position and it will let the LW fill to water surface level. Auto will allow the fill from the lake to be closed and the LW aerator pump to control the level up to the overflow. Recirc will allow the LW water to be recirced if you have fish you want to keep alive while traveling down the road. Just leave the LW pump switch ON in the recirc position and your catch will remain frisky with fresh bubbled water. If you dont have a 3 way switch you will have to plug the LW to keep water while traveling. But on the water the LW pump should be sufficent to keep your level high enough and keep your catch alive. Hope this helps just alittle....Ranger
Mark McGuire 918-441-1453
Guiding on Eufaula, Tenkiller, and Ft Gibson
Crazy Angler Pro Staff
Fle Fly Outdoor Brandz Pro Staff & VIP Team Cordinator