Bighorn 3185 Fresh Water Tank


I tried to fill my fresh water tank time so that I could sanitize it. According to the owner's manual, it has a 75 gallon tank but using a flow meter to measure the amount of water, was only able to put in about 50 gallons before it started coming out of the overflow. I checked the freshwater guage and it registered 2/3rds full. I am the third owner and the unit has had very little use. Last year I tried to fill the tank and discovered that the tank connections were crossed up and as the tank filled, the weight of the water pulled the connectors out of the tank wall. I replaced the plastic connectors with brass fittings. During last season, I only carried about 10 gallons of water for roadside potty stops. Any ideas why it only seems to hold 50 gallons? When I worked on it last year, the tank filled the available space so it seems like the correct tank.



Well-known member
According to the specs I saw your capacity is supposed to be in the low 70s range. I have found over the past four heartland fivers, that the tanks rarely fill to the exact specs. My landmark was to have 105 gallon capacity and I never could get more than mid 70s capacity according to my flow meter, water meter in it as I filled it to the over flows. Now keep in mind the max capacity stated includes the 12 gallons in the water heater per the factory specs. Plus to get fully full you would need to be perfectly level as well, otherwise it will run out of the overflows.


Well-known member
If your tank is gravity filled, you probably have water trapped in the overflow/vent tube. Get a short piece of tubing about the same size as the overflow tube and blow out the overflow tube. You should hear water gurgling when filling from the vent tube.