Installation of a second water tank

Reading time 4 minutes

Updated – December 30, 2022

There is a practical recess in the false floor between the shower and bathroom, including a floor hatch. There is space for a second 150 liter water tank. It is flush with the rear wall in the rear garage.

Laying the various hose connections turns out to be tricky. In preparation, a rectangular recess of approx. 70 x 110 mm must be made in the existing partition on the driver's side, as well as an approx. 30 mm hole on the passenger side, suitable for the 19 mm connection of the extraction hose. The 12 mm ventilation hose can be routed through the existing recess in the fresh water piping at the top on the driver's side and is connected to a 90° angle connection built into the tank top from below, which is countered flush from above, and secured using a hose clamp.

A 40 mm hose that fits onto the provided connection pieces is used to connect to the filler neck. This is connected to the built-in standard water tank in the vanity unit using DN40 HT piping. The connection to the hose is made using a DN40 T-piece inserted into the existing tank and suitable elbow pieces. Please note that the pipe routing runs continuously.

The 40 mm hose is pushed underneath the exhaust hose of the heater towards the additional tank. There it opens into a 90° angle that is welded together with two sleeves, onto which the hose is pushed and fixed with appropriate hose clamps.

The attachment of the exhaust hose can be set lower to provide more storage space below the sink. Accordingly, a cladding must be created in order to prevent small parts from disappearing unintentionally on the lower floor either through the existing cutout for the faucet supply lines, the sink waste pipe, or the exhaust pipe cutout in the shelf.
Do not screw on the rear right wooden bracket, otherwise the board can no longer be removed. So you raise it to the left by about 30 degrees and you can take it out. The front vertical board is just plugged in. This provides easy access to the HT piping.

The 12 mm ventilation hose reaches this area below the exhaust pipe. A piece of hose approximately 12 cm long is cut out of the existing ventilation hoses at a suitable location. The ends are guided with suitable reducers on the right and left to a corresponding T-hose connector, the center connection of which is plugged onto the 12 mm ventilation hose and firmly connected using a hose clamp.

Ultimately, all that remains is to connect the 19 mm supply hose. In preparation, the three drawers are removed by loosening the fastening screws on both sides of the side drawer pull-out rails in the kitchen cupboard. The cabinet base is removed after loosening the four screw connections in the corners. Access to the tubing is now free.

The entire surrounding area can be cleaned and the sieve installed on the input side of the high-pressure pump for the fresh water supply can be cleaned. First, empty all the water and keep a towel to absorb any remaining water.

The cap containing the feeding tube is unlocked by turning the bayonet lock counterclockwise and removed from the holder by gently pulling. After cleaning both parts with a brush and vacuum cleaner, and also cleaning the built-in O-ring on the cap, everything is reassembled in the opposite sense and the bayonet lock is closed by turning it clockwise.

Here too, a piece of hose measuring around 12 cm is cut out of the hose leading to the pump. Using suitable reducers, the free hose ends are routed to a Y-hose connector and secured with hose clamps to ensure parallel water extraction from both tanks.

By connecting both tanks in parallel, the tank contents on the display remain accurate.

Now that everything is in place, remove the tank again. Why? Well, a possible flood outside the RV is certainly more time- and labor-saving than experiencing it inside the RV. The possible problem is not the hose connections, but the cleaning opening. This is usually relatively difficult to get sealed. An effective trick helps here: rub the seal, edge of the lid and opening thoroughly with petroleum jelly. Now the cover and the rubber seal slide cleanly onto each other when tightened and a tight screw connection is achieved, but only with appropriate force.

The ventilation screw connection should not be installed with the thin “pseudo seal” provided, but rather with two separate rubber seals, inside and outside.

In this context, it was also explained to me why Niessmann & Bischoff put a white sealant on the corresponding screw connections for the extraction and ventilation opening on their original water tank, which becomes leaky in the long run... instead of installing proper rubber seals.

Finally, set up the tank so that the maximum possible water pressure is on the screw cap and vent screw connection. During the leak test, fix the hoses so that no water can escape through them until the highest filling level has been reached.
Fill the water tank to the maximum, wipe off any drips and wait a while to check whether all screw connections are absolutely tight. If no water comes out, empty the tank and put it back in place. Make all hose connections, secure them and tighten any existing ones if necessary.

During the initial filling, when installed, continually check all hose connections and connections for leaks.

In the HT pipe construction shown for filling, the additional tank is filled first. When this is full, the water runs into the original tank. As mentioned, water is withdrawn from both tanks at the same time.

Switch on the pressure pump and open the taps to vent the system. If water continuously comes out of all taps, they can be closed again. After a few seconds, the pump should have built up enough pressure to switch itself off using the built-in pressure switch.

Finally, check all screw connections of the water supply lines to the tapping points for leaks. If everything is tight, switch off the pump again and reduce the pressure by opening a tapping point.