How to Install a Holding Tank on a Boat

Boat speeding across the surface of the water
  • 2-10 hours
  • Intermediate
  • 65-1,000
What You'll Need
Polyethyleneholding tank
Plastic tubing
Plastic fittings
Tie down strap kit
Phillip's or flathead screwdriver

If you own a boat that will be out on the water for a one day trip or beyond, you will need to holding tank. Having a holding tank on your boat is a common way to ensure you are in compliance with all sewage discharge laws. Most of all, a holding tank removes the complication of sewage handling.

With the proper equipment and tools, installing a holding tank on your own can be done with a few hours of committed time.

Step 1 - Prepare Installation Area

Before purchasing your holding tank, ensure it has not been stored in direct sunlight and it has been protected from freezing conditions. Polyethylene tanks are not subject to retaining odors when they are in use as much as aluminum or stainless steel tanks. To determine how much weight will be secured by your tie down strap kit, you will need to estimate the total weight of the holding tank to include waste. Waste weighs approximately eight pounds per gallon. The restraint should be strong enough to immobilize the holding tank so it will not move when your boat is operating at full speed and encountering waves and rough waters. Use this formula to calculate:

(weight of tank alone)+(the volume gallon tank x 8 lbs.)x2 = total tie down weight.

The tank must be kept at room temperature for at least six hours. The surface of where you will install the tank on your boat should be flat and clean with no protruding screws or nails that may puncture the tank. Ensure the area is supported on all planes by marine plywood.

Step 2 - Place Holding Tank

After the elapsed six hours and preparation of the installation area, you can now place your holding tank. To ensure that the tank will stay in place, secure it to the floor of the boat using the tie down strap kit. To avoid having to remove the straps, make sure all plumbing connections are in the proper position.

Step 3 - Apply Fittings

The next step will be to get all your tubing and fittings connected to prevent points of stress on the tank. When connecting fittings to polyethylene tanks, be sure to follow the manufacturer's instructions. Applying fixtures too tight will cause damage to connection points that will be undetectable at assembly but will become apparent should leaks occur further down the line. Do not tighten fittings more than 1/4 turn with wrench after hand tightening.

Step 4 - Test for Leaks

The holding tank is mounted and fixtures are in place. The last step to be done before the plumbing is completed is to test the unit for leaks. To conduct the test, fill the unit with water and visibly check for leaks around the entire surface. Checking the unit at this stage is important. Two days into your week-long stay on the water is too late to check for leaks.

Step 5 - Prepare Holding Tank for Plumbing

After you test the holding tank for leaks, you can now prepare the unit for plumbing from the toilet. Ensure you have all proper hoses and pumps. If your holding tank is made of polypropylene, metal connections for fittings is not recommended as this will eventually cause leakage problems.