During some battery relocation work I remember noting some access capability from the batt box under the navstation. I want to say there was an access port on the inbd, fwd side of the box. I was focused on getting a pair of golf cart batts to fit the compartment at the time and didn't assess full potential of getting to that connection. If there's no port on your boat, cut a hole and put one in - easier than tank removal! Also the whole box may be removable (didn't pay that much attention either) which would probably be an easier path.
I'm an hour away from the boat but I've glanced up under the nav station before. I remember it being Very tight but I didn't climb into the battery compartment area to truly get a look for possible access. Thanks.
On my 93 C30 the battery compartment is under the aft half of the starboard cabin bench. The water tank is under the forward half of the bench. The tank's water outlet is on the aft end of the tank forward of the battery compartment. It is a tight fit to get to the outlet. I cut the hose off the outlet valve and now cannot get a new hose back on. For now I'm just using the v-berth tank.