According to my manual, for hull#165 and earlier there is a single 50 gallon tank under the stbd settee. On #166 and after there is a 28gal tank under the stbd settee, 22gal under the port dinette, and an optional 35gal under the V berth. Mine has all 3, although she rides a little bow heavy if the v berth is filled so I usually use that one first. The valves to control the individual tanks on mine are located all the way forward under the stbd settee so you can switch from one to the other to maintain balance.
Kevin Wright
E35 III Hydro Therapy